Add age color mapping to blame view

What does this MR do?

Adds a color-coded age map to the blame view showing how new or old different areas of the code are relative to the project.

Are there points in the code the reviewer needs to double check?

1. I calculate the age in reference to the oldest of either the oldest commit on the page or the project created at date. This prevents me from needing to find the oldest commit in the repository but still shows that a file has aged if there was a large time difference between when the repository was created and when it was brought into GitLab.
2. I looked through several other spec files, but really didn't find any tests that quite tested on an array like this one. Was the test approach I took proper?

Why was this MR needed?

There is currently no visual indicator of the age of a file in blame view. Other blame views (e.g. GitHub) provide this features.

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• CHANGELOG entry added
• N/A Documentation created/updated
• N/A API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closes #23998 (closed)