Allow user to commit new files in pipeline editor

What does this MR do?

This changes how graphQL mutations work on the FE to commit files. We check if we should create a new file or update an existing one, so users can now create new files if required.

If you want to test it locally:

• Enable flag pipeline_editor_empty_state_action
• Create a new project
• Go in the pipeline editor section (CI/CD => Editor)
• You will see an empty state
• Click "get started"
• Add any text in the editor
• Commit the file
• Notice the success message!
• Change the content again
• Commit again
• Should also give you a success message

Note: When typing content in the editor in a project without a repository, you will get a linting error. This is currently being worked on from the BE side: #323223 (closed)

Screenshots (strongly suggested)

Commits

Does this MR meet the acceptance criteria?

Conformity

• 📋 Does this MR need a changelog?
  • [-] I have included a changelog entry.
  • I have not included a changelog entry because this is behind a disabled feature flag.
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• Separation of EE specific content

Availability and Testing

We need to make sure the commit functionality keeps working as intented.

• 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