Removing deprecated charset=utf-8 from Content-Type header

[vikrama]

Addresses #2882 . Keeping the string in api module as per Martin's suggestion.

[apollo-cla]

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[martinbonnin]

@vikrama Thanks for the contribution 🤗

I moved everything to the api.internal package, I don't think this needs to be seen from consumers. We can always add it later if needed.

[vikrama]

Thx @martinbonnin for the review.

Not urgent, but trying to understand why my last build failed. Seems unrelated to my changes. Will help me be better informed while sending PRs in the future.

[martinbonnin]

trying to understand why my last build failed. Seems unrelated to my changes. Will help me be better informed while sending PRs in the future.

Are you refering about this build failure? https://github.com/apollographql/apollo-android/runs/1724495722

This is because we track changes to the public API with metalava https://android.googlesource.com/platform/tools/metalava/

This we we're notified any time the public API breaks. For this to work, we also have to track we new additions are made like is the case here.

To fix the build, you can run ./gradlew metalavaGenerateSignature and commit the updates api.txt files