feat: Programmatic download of valid ZIP files returns HTML responses for certain producer URLs

[cka-y]

Summary:
Added User-Agent to the header of the requests, resolving the issue for all feeds specified in #502. To achieve this, I mimicked the equivalent curl request from the browser network tab and systematically filtered out each header to identify that only the User-Agent was necessary.

Testing Tips:

• Run datasets-batch-deployer-dev from the branch feat/502 to deploy the current behavior.
• Adjust the FEEDS_LIMIT variable in the batch-datasets-dev cloud function to cover more feeds.
• Filter logs to validate that feeds mdb-232, mdb-919, and mdb-683 have been properly processed. If these feeds are not included in the processing, you may need to further increase the FEEDS_LIMIT variable.

Example for mdb-683:

Please make sure these boxes are checked before submitting your pull request - thanks!

• Run the unit tests with ./scripts/api-tests.sh to make sure you didn't break anything
• Add or update any needed documentation to the repo
• Format the title like "feat: [new feature short description]". Title must follow the Conventional Commit Specification(https://www.conventionalcommits.org/en/v1.0.0/).
• Linked all relevant issues
• Include screenshot(s) showing how this pull request works and fixes the issue(s)

[davidgamez]

Some source systems prefer that we send a customized user agent to identify us as downloaders (see MobilityData/gtfs-validator#1562). I'm okay with this solution for now; let's just keep in mind that this issue can appear again, and we might need a less simple solution.