Enforcing prometheus labels for the SLI metrics

What does this MR do and why?

Missing request_urgency for the gitlab_sli_rails_request_error_total metric broke staging when feature flag gitlab_metrics_error_rate_sli was enabled.

{"timestamp":"2022-12-01T14:44:18.716Z","pid":1,"message":"! Unable to load application: Prometheus::Client::LabelSetValidator::InvalidLabelSetError: labels must have the same signature: (expected keys: [:endpoint_id, :feature_category, :request_urgency], got: [:endpoint_id, :feature_category])"}
/srv/gitlab/vendor/bundle/ruby/2.7.0/gems/prometheus-client-mmap-0.16.2/lib/prometheus/client/label_set_validator.rb:40:in `validate': labels must have the same signature: (expected keys: [:endpoint_id, :feature_category, :request_urgency], got: [:endpoint_id, :feature_category]) (Prometheus::Client::LabelSetValidator::InvalidLabelSetError)
from /srv/gitlab/vendor/bundle/ruby/2.7.0/gems/prometheus-client-mmap-0.16.2/lib/prometheus/client/metric.rb:72:in `label_set_for'
from /srv/gitlab/vendor/bundle/ruby/2.7.0/gems/prometheus-client-mmap-0.16.2/lib/prometheus/client/counter.rb:16:in `increment'
from /srv/gitlab/lib/gitlab/metrics/sli.rb:57:in `increment'
from /srv/gitlab/lib/gitlab/metrics/sli.rb:97:in `increment'
from /srv/gitlab/lib/gitlab/metrics/requests_rack_middleware.rb:131:in `record_error'
from /srv/gitlab/lib/gitlab/metrics/requests_rack_middleware.rb:86:in `call'
from /srv/gitlab/vendor/bundle/ruby/2.7.0/gems/gitlab-labkit-0.29.0/lib/labkit/middleware/rack.rb:19:in `block in call'
from /srv/gitlab/vendor/bundle/ruby/2.7.0/gems/gitlab-labkit-0.29.0/lib/labkit/context.rb:36:in `with_context'
from /srv/gitlab/vendor/bundle/ruby/2.7.0/gems/gitlab-labkit-0.29.0/lib/labkit/middleware/rack.rb:18:in `call'
from /srv/gitlab/vendor/bundle/ruby/2.7.0/gems/actionpack-6.1.6.1/lib/action_dispatch/middleware/request_id.rb:26:in `call'
from /srv/gitlab/vendor/bundle/ruby/2.7.0/gems/sentry-raven-3.1.2/lib/raven/integrations/rack.rb:51:in `call'
from /srv/gitlab/vendor/bundle/ruby/2.7.0/gems/railties-6.1.6.1/lib/rails/engine.rb:539:in `call'
from /srv/gitlab/vendor/bundle/ruby/2.7.0/gems/railties-6.1.6.1/lib/rails/railtie.rb:207:in `public_send'
from /srv/gitlab/vendor/bundle/ruby/2.7.0/gems/railties-6.1.6.1/lib/rails/railtie.rb:207:in `method_missing'
from /srv/gitlab/lib/gitlab/middleware/release_env.rb:13:in `call'
from /srv/gitlab/vendor/bundle/ruby/2.7.0/gems/rack-2.2.4/lib/rack/urlmap.rb:74:in `block in call'
from /srv/gitlab/vendor/bundle/ruby/2.7.0/gems/rack-2.2.4/lib/rack/urlmap.rb:58:in `each'
from /srv/gitlab/vendor/bundle/ruby/2.7.0/gems/rack-2.2.4/lib/rack/urlmap.rb:58:in `call'
from /srv/gitlab/vendor/bundle/ruby/2.7.0/gems/rack-2.2.4/lib/rack/mock.rb:84:in `request'
from /srv/gitlab/vendor/bundle/ruby/2.7.0/gems/rack-2.2.4/lib/rack/mock.rb:57:in `get'
from /srv/gitlab/config.ru:9:in `block (2 levels) in <main>'
from /srv/gitlab/vendor/bundle/ruby/2.7.0/gems/rack-2.2.4/lib/rack/builder.rb:236:in `to_app'
from /srv/gitlab/vendor/bundle/ruby/2.7.0/gems/rack-2.2.4/lib/rack/builder.rb:117:in `new_from_string'
from /srv/gitlab/vendor/bundle/ruby/2.7.0/gems/rack-2.2.4/lib/rack/builder.rb:105:in `load_file'
from /srv/gitlab/vendor/bundle/ruby/2.7.0/gems/rack-2.2.4/lib/rack/builder.rb:66:in `parse_file'
from /srv/gitlab/vendor/bundle/ruby/2.7.0/gems/puma-5.6.5/lib/puma/configuration.rb:348:in `load_rackup'
from /srv/gitlab/vendor/bundle/ruby/2.7.0/gems/puma-5.6.5/lib/puma/configuration.rb:270:in `app'
from /srv/gitlab/vendor/bundle/ruby/2.7.0/gems/puma-5.6.5/lib/puma/runner.rb:150:in `load_and_bind'
from /srv/gitlab/vendor/bundle/ruby/2.7.0/gems/puma-5.6.5/lib/puma/cluster.rb:357:in `run'
from /srv/gitlab/vendor/bundle/ruby/2.7.0/gems/puma-5.6.5/lib/puma/launcher.rb:193:in `run'
from /srv/gitlab/vendor/bundle/ruby/2.7.0/gems/puma-5.6.5/lib/puma/cli.rb:81:in `run'
from /srv/gitlab/vendor/bundle/ruby/2.7.0/gems/puma-5.6.5/bin/puma:10:in `<top (required)>'
from /srv/gitlab/vendor/bundle/ruby/2.7.0/bin/puma:25:in `load'
from /srv/gitlab/vendor/bundle/ruby/2.7.0/bin/puma:25:in `<top (required)>'
from /usr/lib/ruby/gems/2.7.0/gems/bundler-2.3.15/lib/bundler/cli/exec.rb:58:in `load'
from /usr/lib/ruby/gems/2.7.0/gems/bundler-2.3.15/lib/bundler/cli/exec.rb:58:in `kernel_load'
from /usr/lib/ruby/gems/2.7.0/gems/bundler-2.3.15/lib/bundler/cli/exec.rb:23:in `run'
from /usr/lib/ruby/gems/2.7.0/gems/bundler-2.3.15/lib/bundler/cli.rb:483:in `exec'
from /usr/lib/ruby/gems/2.7.0/gems/bundler-2.3.15/lib/bundler/vendor/thor/lib/thor/command.rb:27:in `run'
from /usr/lib/ruby/gems/2.7.0/gems/bundler-2.3.15/lib/bundler/vendor/thor/lib/thor/invocation.rb:127:in `invoke_command'
from /usr/lib/ruby/gems/2.7.0/gems/bundler-2.3.15/lib/bundler/vendor/thor/lib/thor.rb:392:in `dispatch'
from /usr/lib/ruby/gems/2.7.0/gems/bundler-2.3.15/lib/bundler/cli.rb:31:in `dispatch'
from /usr/lib/ruby/gems/2.7.0/gems/bundler-2.3.15/lib/bundler/vendor/thor/lib/thor/base.rb:485:in `start'
from /usr/lib/ruby/gems/2.7.0/gems/bundler-2.3.15/lib/bundler/cli.rb:25:in `start'
from /usr/lib/ruby/gems/2.7.0/gems/bundler-2.3.15/exe/bundle:48:in `block in <top (required)>'
from /usr/lib/ruby/gems/2.7.0/gems/bundler-2.3.15/lib/bundler/friendly_errors.rb:117:in `with_friendly_errors'
from /usr/lib/ruby/gems/2.7.0/gems/bundler-2.3.15/exe/bundle:36:in `<top (required)>'
from /srv/gitlab/bin/bundle:5:in `load'
from /srv/gitlab/bin/bundle:5:in `<main>'

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How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.