Initial investigation into supporting HTTP/2

[alzimmermsft]

Description

Investigation into supporting HTTP/2 in Azure SDKs.

The current design thought is allowing an EnumSet of versions to be passed to declare which protocols the underlying HTTP stack can use when making requests. Given the ubiquity of HTTP/1.1 it must always be included.

Only HTTP/2 is added in addition to HTTP/1.1 as HTTP/3 / QUIC isn't implemented consistently across the HTTP stacks we provide.

All SDK Contribution checklist:

• The pull request does not introduce [breaking changes]
• CHANGELOG is updated for new features, bug fixes or other significant changes.
• I have read the contribution guidelines.

General Guidelines and Best Practices

• Title of the pull request is clear and informative.
• There are a small number of commits, each of which have an informative message. This means that previously merged commits do not appear in the history of the PR. For more information on cleaning up the commits in your PR, see this page.

Testing Guidelines

• Pull request includes test coverage for the included changes.

[azure-sdk]

API change check

APIView has identified API level changes in this PR and created following API reviews.

com.azure:azure-core-http-jdk-httpclient
com.azure:azure-core-http-netty
com.azure:azure-core-http-okhttp
com.azure:azure-core-http-vertx
com.azure:azure-core