Replace Rails content_type header with media_type

[hannahramadan]

A change in Rails 6.1 -> Rails 7 includes ActionDispatch::Request#content_type now returns Content-Type header as it is.

Where the call request.content_type used to return 'text/csv' in Rails 6, it now returns the entire header, something like 'text/csv;header=present;charset=utf-16' in Rails 7. To return just the MIME type, one woud call request.media_type. This is what the agent is expected to send via spec. Definition.

We should replace calls to request.content_type with request.media_type. We should confirm request.media_type exists in older Rails versions. Already confirmed in Rails 6.

Discovered in #2500

[workato-integration]

https://new-relic.atlassian.net/browse/NR-248625