Http2 adatper header support dynamic

[Passer-by]

New Pull Request Checklist

• I have read the Documentation
• I have searched for a similar pull request in the project and found none
• I have updated this branch with the latest main branch to avoid conflicts (via merge from master or rebase)
• I have added the required tests to prove the fix/feature I'm adding
• I have updated the documentation (if necessary)
• I have run the tests without failures
• I have updated the CHANGELOG.md in the corresponding package

[Passer-by]

Dio's header is of type Map<String, dynamic>, so the Http2Adapter cannot directly convert the value to a string.
But there is a question about this PR: Why does Dio perform a default trim operation on the value? Unlike the native Dart HttpClient, which does not trim when setting headers. Should I adhere to Dio's standard or the Dart HttpClient standard?

[AlexV525]

Should I adhere to Dio's standard or the Dart HttpClient standard?

Thanks for details. I think we should stick to RFCs instead of Dio's. We'll manage to get rid of the Dio's implementation too.