Usage data usage_activity_by_stage feature flags

What does this MR do?

1. Makes the usage_ping_batch_counter flag default enabled, and keeps it as a safeguard

• We did extensive testing on gitlab.com and self-hosted environments https://gitlab.com/gitlab-org/telemetry/issues/308 https://gitlab.com/gitlab-org/telemetry/issues/309
• We optimize individual queries for gitlab.com scale which is > 10x larger than any other #205281 (closed)
• Individual queries have a fallback of -1 and don't break the whole usage ping !26381 (merged)
• On largest known self-hosted instances we expect all of the usage ping to be computed in 1 hour or less https://gitlab.com/gitlab-org/telemetry/issues/309#on-largest-known-self-hosted-instances-we-expect-all-of-the-usage-ping-to-be-computed-in-1-hour-or-less

2. Removes the :usage_activity_by_stage_monthly and makes the usage_activity_by_stage as the single toggle for both cases

• We have made extensive analysis on batch counter and their performance on gitlab.com and self-hosted instances https://gitlab.com/gitlab-org/telemetry/issues/308 https://gitlab.com/gitlab-org/telemetry/issues/309
• usage_activity_by_stage is still the toggle to safeguard for troubles.

3. Removes additional ::Gitlab.com? check as :usage_activity_by_stage is enough

• For gitlab.com we have already non-usage ping dashboards https://app.periscopedata.com/app/gitlab/604621/GitLab.com-SMAU
• For gitlab.com we have (can in the future) disabled the ping https://gitlab.com/gitlab-com/gl-infra/infrastructure/issues/9385#note_299046669
• We can disable the feature flag usage_activity_by_stage when needed

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

Closes #208892 (closed)