Merge redundant `Authorization` and `Content-Type` headers

[philsturgeon]

Summary

Sometimes people add the Authorization header so they can add an example, so we would want to make sure them adding a new one (Authorization or authorization) would be merged in with anything from securityScheme which should provide a Authorization header too.

They also do the same with Content-Type, which is already set by the dropdown on the request body.

Acceptance Criteria

1. Make sure authentication is merging successfully (case insensitive), and example is being used if provided
2. Try it and Request Samples all agree on what Authentication is.
3. Content-Type is only controlled via the request body dropdown in the main column, and does not show up as a regular parameter in Try It, and the request body dropdown value is used in Request Samples