chore: Removes boundary from accept header

[calvincestari]

This is the same as #232 but limited to non-subscription operations and to be merged into the feature/defer-execution-networking branch to only be applicable once all the defer work is merged into main.

The boundary portion of the accept header has no effect on the boundary in the received multipart response so we can remove it and send less data in the request. The multipart response handler is already built to handle any value sent back as the boundary and use that to parse the chunks.

More details in apollographql/router#4395 and apollographql/router#4447.

[calvincestari]

I'm going to go ahead and merge this with the test failure because the test failure is caused by a warning in the test codegen configuration job. The warning is about unused property assignments that will be handled in PR #217 as part of review feedback.

/Users/runner/work/apollo-ios-dev/apollo-ios-dev/apollo-ios/Sources/Apollo/MultipartResponseDeferParser.swift:67:16: error: value 'hasNext' was defined but never used; consider replacing with boolean test
if let hasNext = object.hasNext {
~~~~^~~~~~~~~~
!= nil
/Users/runner/work/apollo-ios-dev/apollo-ios-dev/apollo-ios/Sources/Apollo/MultipartResponseDeferParser.swift:71:16: error: value 'incremental' was defined but never used; consider replacing with boolean test
if let incremental = object.incremental {
~~~~^~~~~~~~~~~~~~
!= nil