Add Http/2 support in Netty Server

[pujagani]

Description

Add support for Http/2 in the Netty server. It is related to #8719.

Motivation and Context

Current Netty Server supports Http/1.1 for secure communication. The changes add support for Http/2 for a client requesting the use of Http/2.
This will allow clients to leverage features of Http/2 where a single connection is used along with streams for communication.
Netty supports stream multiplexing but leveraging child channels i.e. every new stream has a dedicated child channel.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• I have read the contributing document.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

[shs96c]

I think we can probably simplify the logic of the stream initialisation, and make better use of the existing code we have, particularly when it comes to converting from Netty's http primitives to Selenium's.

[shs96c]

This is mirroring the functionality of the RequestConverter, but requires http object aggregation in order to work, and so is likely to lead to problems when there's very little memory. In addition, it duplicates logic from that class, making fixing discovered issues more work and opening us up to forgetting to change both places.

I'd suggest deleting this and using RequestConverter

[pujagani]

Thank you for pointing it out. Since Http/2 uses frames with stream ids, I am leveraging to Http2StreamFrameToHttpObjectCodec get the HttpObject to pass it to Selenium handlers. I have moved the Http/2 request handling to RequestConverter.

[shs96c]

These should be added to the SeleniumInitializer

[pujagani]

We are using Http2MultiplexHandler for Http/2 support of streams. It leverages child channels of Netty. The handler takes in only a single handler to be added for child channels and their respective channel context. In order to add multiple handlers, Http2StreamInitializer was created. An instance of this sharable handler is passed while creating Http2MultiplexHandler.