Exclude ops without error rate from error budget

For gitlab-com/gl-infra/scalability#1500 (closed)

This excludes operation rates from the error budget for stage groups calculations for components that do not have an error rate.

The previous approach (!4096 (merged)) marked these operations as successes. Which is not entirely correct, because we can't actually know if the operation was a success.

Furthermore, all SLIs require an operation rate to be defined, but not an apdex or an error rate. This means that the rails_requests component we recently added would count all requests as a success on that front.

This affects the following groups: (✔ means manually validated that the result is in line with the expectation).

Corrected Snapshot	Version with superfluous aggregation	Current	Expected decrease on 2022-01-01
global_search	global_search	global_search	-0.1126% ✔
package	package	package	-0.0087% ✔
pipeline_authoring	pipeline_authoring	pipeline_authoring	-0.0257% ✔
pipeline_execution	pipeline_execution	pipeline_execution	-0.0042% ✔
release	release	release	-0.0088% ✔
workspace	workspace	workspace	-0.0041% ✔