Don't execute webhooks/services when above limit

What does this MR do?

If a single push has a number of changes over the threshold (push_event_hooks_limit setting, 3 by default), the related project webhooks and services won't be executed.

This way, in an event where bulk changes are pushed, the system won't be overloaded.

git_push_execute_all_project_hooks feature flag has been added so instance admins can choose to disable this behavior and still allow executing all project hooks regardless of number of changes.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• [-] Separation of EE specific content

Performance 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

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

#31009 (closed)