Audit required approvals changes at Project Level

What does this MR do?

This MR will ensure audit event is recorded both in DB and log file when user successfully update no. of required approvals at Project level. We would like to capture changes to ApprovalProjectRule model and surface it under Project audit events page. The audit event will be recorded for update issued via both App and API.

As part of this MR, I have also:

• Addressed a bug that causes changes audit event recorded on creation instead of update. This is an existing issue and need to be fixed before this new audit event is added.
• Extended for_changes method to accept reference of target object being audited. Previously the entity is used to record both scope and target change object. While that is true in some context (i.e. the target model happens to be a User/Project/Group), it does not work for ApprovalProjectRule (i.e. the target model is ApprovalProjectRule and the entity is the Project)

Quick rehash on naming in AuditEventService class:

Name	Meaning
Entity	The scope (User/Project/Group) this audit event belongs to
Model	The target object being audited

How the event attributes are mapped to the Audit Events view

Parent issue #7531 (closed)

Screenshots

Project-level

(Project > Settings > Audit Events)

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Instance-level

(Admin Area > Monitoring > Audit Log)

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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