Enable Git streaming audit events in all offerings

What does this MR do and why?

Currently, the needs_audit field controls if we should use the new workflow of Git clone/fetch streaming audit events. According to the implementation plan, the logic behind this field does the following:

1. If SaaS, then returns false (we just support Self Managed now)
2. Only when FF is opened and project group has set the streaming audit event，then returns true
3. All any other case return false

We want to change this logic since:

• This audit event should NOT only exist for self-managed, so we would like to remove the SaaS validation.
• We don't need to validate if project.group.external_audit_event_destinations exists in this step. Currently, we support two types of audit streaming events: For instances and top-level groups. We should delegate this validation to the AuditEvents::ExternalDestinationStreamer class that determines if the stream audit event is streamable (if it is created by an instance or top-level group, has the licensing capabilities, active audit event destinations, etc.) in this step.

References

• Discussion: #415138 (comment 2589130360)
• Feature: Support to detect git clone/pull audit event (!123486 - merged)

How to set up and validate locally

• Enable the log_git_streaming_audit_events FF.
• Set up the audit event streaming for HTTP destination (https://docs.gitlab.com/user/compliance/audit_event_streaming/#add-a-new-http-destination). You can use https://webhook.site for this purpose.
• Perform a Git clone operation of a local repository.
• Check https://webhook.site. The Git stream audit event should be created and the verb field included.

MR acceptance checklist

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Related to #553801 (closed)