Support JOB-TOKEN authentication header for generic packages

What does this MR do and why?

This MR adds authentication support using both JOB-TOKEN and Basic Authentication headers for Generic packages. Related issues:

• #374564
• !111751
• #392760
• #212181

Screenshots or screen recordings

NA

⚗ How to set up and validate locally

1️⃣ With CI

1. Create a project with the following .gitlab-ci.yml file:

   image: curlimages/curl:latest
   
   stages:
     - upload
     - download
   
   upload:
     stage: upload
     script:
       - 'echo "bananas!" > file.txt'
       - 'curl --header "JOB-TOKEN: $CI_JOB_TOKEN" --upload-file ./file.txt "${CI_API_V4_URL}/projects/${CI_PROJECT_ID}/packages/generic/my_package/0.0.1/file.txt"'
   
   download_using_header:
     stage: download
     script:
       - 'curl --header "JOB-TOKEN: $CI_JOB_TOKEN" "${CI_API_V4_URL}/projects/${CI_PROJECT_ID}/packages/generic/my_package/0.0.1/file.txt"'
   
   download_using_job_token_query_param:
     stage: download
     script:
       - 'curl "${CI_API_V4_URL}/projects/${CI_PROJECT_ID}/packages/generic/my_package/0.0.1/file.txt?job_token=${CI_JOB_TOKEN}"'
   
   download_using_runner_token_query_param:
     stage: download
     script:
       - 'curl "${CI_API_V4_URL}/projects/${CI_PROJECT_ID}/packages/generic/my_package/0.0.1/file.txt?token=${CI_JOB_TOKEN}"'
   
   download_using_basic_auth:
     stage: download
     script:
       - 'curl --user "gitlab-ci-token:${CI_JOB_TOKEN}" "${CI_API_V4_URL}/projects/${CI_PROJECT_ID}/packages/generic/my_package/0.0.1/file.txt"'

2. Commit and watch the runner do its thing 🍿

2️⃣ with $ curl

• Have a PAT ready.
• Run the previous scenario to at least publish the generic package to the project's generic registry.

Let's check with the header:

$ curl --header "PRIVATE-TOKEN: <pat>" "http://gdk.test:8000/api/v4/projects/<project_id>/packages/generic/my_package/0.0.1/file.txt"
bananas!

Let's check with basic auth (inline form):

$ curl "http://<username>:<pat>@gdk.test:8000/api/v4/projects/<project_id>/packages/generic/my_package/0.0.1/file.txt" 
bananas!

MR acceptance checklist

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

• I have evaluated the MR acceptance checklist for this MR.