Rename Instance Administration project

What does this MR do?

Rename the "Instance Administration project" to "Self monitoring project".

This MR:

1. Renames the belongs_to association in the ApplicationSetting model from instance_administration_project to self_monitoring_project.
2. Adds an alias_attribute :instance_administration_project_id :self_monitoring_project_id to the ApplicationSetting model. The column will be renamed in another MR and the alias_attribute will be removed.
3. Renames all references to instance_administration_project to self_monitoring_project.
4. Renames "Instance Administration project" to "Self monitoring project" in docs.

Issue: #42628 (closed)

Screenshots

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

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