Stop log content type determination when downloading packages

What does this MR do and why?

Based on the discussion about generic package content types, we decided to create an allow list for content types.

In order to do that, we started to collect all the possible content types with this MR, after 1 week, we've collect sufficient data that allows us to build the allow list.

👉🏻 See more detail data in this comment

This MR stops logging content type determination, removes the usages and definition of FF packages_generic_package_content_type.

References

• #547424 (closed)

Screenshots or screen recordings

N/A

How to set up and validate locally

1. Switch to this branch 444768-stop-log-content-types
2. Enter Rails console and try to enable the feature flag

   Feature.enabled?(:packages_generic_package_content_type)
   => Feature::InvalidFeatureFlagError: Missing type for undefined feature `packages_generic_package_content_type`

3. Exit Rails console and start to monitor application_json.log

   tail -f log/application_json.log

4. Enter Package Registry page and try to download a file OR download the file by generic package file endpoint

   curl -L --header "PRIVATE-TOKEN: ${TOKEN}" \
     "${GITLAB_URL}/api/v4/projects/${PROJECT_ID}/packages/generic/path/to/path/filename.extension" \
     --output filename.extension

5. Verify no content type determination logs appear

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Related to #444768