Allow routing rules to contain shard information

What does this MR do?

This MR updates the gitlab.yml.erb to allow routing rules to contain shard information.

This change is behind a feature flag and is not released to end-users, but is required for gitlab.com to correctly configure our chef nodes, in particular, the console and deployer nodes.

The functionality was added in gitlab!145495 (merged).

Test plan

1. Set up omnibus locally or on a VM (i used the VM route). I followed the steps in https://gitlab.com/gitlab-org/omnibus-gitlab/-/blob/master/doc/development/setup.md#get-the-source-of-omnibus-gitlab too
2. Run sudo cat /var/opt/gitlab/gitlab-rails/etc/gitlab.yml and ensure that no sidekiq.routing_rule is present

## Sidekiq
  sidekiq:
    log_format: json

3. Update the attributes file

schin@instance-20240403-012622:~/omnibus-gitlab/files/gitlab-cookbooks$ cat /etc/gitlab/gitlab.rb | grep routing_rule
default['gitlab']['sidekiq']['routing_rules'] = [["resource_boundary=cpu", "cpu_boundary"],['*', 'default', 'testing']]

4. Run sudo gitlab-ctl reconfigure and verify the gitlab.yml renders rules with shard information.

 ## Sidekiq
  sidekiq:
    log_format: json
    routing_rules:
      - ["resource_boundary=cpu", "cpu_boundary"]
      - ["*", "default", "testing"]

Related issues

gitlab-com/gl-infra/scalability#3385

Checklist

See Definition of done.

For anything in this list which will not be completed, please provide a reason in the MR discussion.

Required

• MR title and description are up to date, accurate, and descriptive.
• MR targeting the appropriate branch.
• Latest Merge Result pipeline is green.
• When ready for review, MR is labeled "~workflow::ready for review" per the Distribution MR workflow.

For GitLab team members

If you don't have access to this, the reviewer should trigger these jobs for you during the review process.

• The manual Trigger:ee-package jobs have a green pipeline running against latest commit.
• If config/software or config/patches directories are changed, make sure the build-package-on-all-os job within the Trigger:ee-package downstream pipeline succeeded.
• If you are changing anything SSL related, then the Trigger:package:fips manual job within the Trigger:ee-package downstream pipeline must succeed.
• If CI configuration is changed, the branch must be pushed to dev.gitlab.org to confirm regular branch builds aren't broken.

Expected (please provide an explanation if not completing)

• Test plan indicating conditions for success has been posted and passes.
• Documentation created/updated. -- the feature is behind a feature flag so the documentation on gitlab rails will be added it is ready to be released for self-hosted users
• Tests added.
• Integration tests added to GitLab QA.
• Equivalent MR/issue for the GitLab Chart opened. -- gitlab-org/charts/gitlab!3682 (merged)
• Validate potential values for new configuration settings. Formats such as integer 10, duration 10s, URI scheme://user:passwd@host:port may require quotation or other special handling when rendered in a template and written to a configuration file.