fix(java): Remove Content-Type from headers when request has no body

[jsklan]

Description

Previously we were including the following header on all requests without a body:

{ 'Content-Type': 'application/json'}

This causes some issues for some APIs since it doesn't respect their API constraints.
Root cause was that the java sdk generator was adding a content type header whenever specific response types were specified in the request.

Changes Made

• Removed consideration of the response type in the sendContent evaluation
• Ensured all places the Content-Type header was added were conditional on the sendContent boolean
• Manual file changes are limited to this file list. Remainder of changes were generated.
  • AbstractEndpointWriter.java
  • OnlyRequestEndpointWriter.java

Testing

Ran seed test --fixture exhaustive --skip-scripts and reviewed the changes manually.

• Unit tests added/updated
• Manual testing completed

[github-actions]

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[jsklan]

@dsinghvi Looks like these changes caused seed snapshot tests to fail. But in this case, the changes are correct per the new changes. How do I mark that the new values are expected so that these tests pass again?