fix: missing headers for feeds mdb-3237 to mdb-3293 and mdb-2939

[cka-y]

Summary:

This pull request introduces a hotfix to address issues with downloading certain GTFS feeds whose producers block the default HTTP headers. The main change is the addition of a custom http_headers override for a specific range of feeds.

Database migration and configuration:

• Added a new migration, hotfix_missing_header.sql, to insert a custom User-Agent and Referer header override for feeds with stable IDs from mdb-3237 to mdb-3293 and mdb-2939, ensuring successful downloads from producers that block the default headers. (liquibase/changes/hotfix_missing_header.sql)
• Updated the main Liquibase changelog (changelog.xml) to include the new hotfix migration, ensuring it is applied in the correct order. (liquibase/changelog.xml)
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