Expose git blame in api

What does this MR do?

This merge request exposes git blame available in web version in GitLab API.

Fixes #51345 (closed).

Example request

GET /api/v4/projects/49/repository/files/files%2Fruby%2Fpopen%2Erb/blame

Example response

[
  {
    "commit": {
      "id": "913c66a37b4a45b9769037c55c2d238bd0942d2e",
      "message": "Files, encoding and much more\n\nSigned-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>\n",
      "parent_ids": [
        "cfe32cf61b73a0d5e9f13e774abde7ff789b1660"
      ],
      "authored_date": "2014-02-27T08:14:56.000Z",
      "author_name": "Dmitriy Zaporozhets",
      "author_email": "dmitriy.zaporozhets@gmail.com",
      "committed_date": "2014-02-27T08:14:56.000Z",
      "committer_name": "Dmitriy Zaporozhets",
      "committer_email": "dmitriy.zaporozhets@gmail.com"
    },
    "lines": [
      "require 'fileutils'",
      "require 'open3'",
      ""
    ]
  }
]

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

Git blame is a heavy operation and may potentially result in Denial of Service if used on big repositories.

• 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