Draft: Adds Secure Files to Runner job request

What does this MR do and why?

This MR adds Secure Files data to the runner job request API endpoint as part of #365050 (closed)

The Runner change is in this MR: gitlab-runner!3695 (closed)

Note: this is an early draft MR for feedback on the approach, testing and polish is still needed.

Sample Output:

[
  {
    "name": "sample.cer",
    "download_url": "http://127.0.0.1:3001/api/v4/projects/24/secure_files/12/download",
    "checksum": "f8c7d7884d4d105701273d17ae0363f35ca61e8975d226d69126170cb058d08c",
    "checusum_algorithm": "sha256"
  
  },
  {
    "name": "sample.p12",
    "download_url": "http://127.0.0.1:3001/api/v4/projects/24/secure_files/14/download",
    "checksum": "b195140806e95786edb2f209a8bb5d00948447523602486d150e5c75a1ae6006",
    "checusum_algorithm": "sha256"
  }
]

Screenshots or screen recordings

https://youtu.be/UPJhZ_9Tdjs

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

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