[release/2.8] feat: Add HTTP2 for unencrypted HTTP (v2)

[erezrokah]

Replaces #4242

Also adds this feature behind an opt-in option to make it non breaking (I don't think it should break things but could be considered a breaking change in the default behavior)

Fixes #4241

You can test via:

docker build . -t registry:v2-h2c
docker run -e REGISTRY_HTTP_H2C_ENABLED='true' -p 5000:5000 registry:v2-h2c

Then on a separate shell:

curl -i --http2-prior-knowledge http://localhost:5000 
HTTP/2 200 
cache-control: no-cache
content-length: 0
date: Fri, 05 Jan 2024 15:40:04 GMT

curl -i http://localhost:5000
HTTP/1.1 200 OK
Cache-Control: no-cache
Date: Fri, 05 Jan 2024 15:40:31 GMT
Content-Length: 0

[erezrokah]

If you're OK with this change for v2 I can port it to v3 as well

[milosgajdos]

I think adding this to v3 would be nice 🤔

[milosgajdos]

@thaJeztah there is something sad happening and I have a feeling it might have to do with the old vendorinig

[erezrokah]

I think adding this to v3 would be nice 🤔

PR for v3 #4248. I used the existing option since v3 is already a major version bump so this way the defaults for TLS and non TLS will be the same

[thaJeztah]

I don't think we should add new features to v2. It's in maintenance mode, so only bug-fixes and security-fixes should go in; other changes should go into v3

[milosgajdos]

I don't think we should add new features to v2. It's in maintenance mode, so only bug-fixes and security-fixes should go in

Yeah, we shouldn't be accepting this to v2

[wy65701436]

I am against and we should consider adding this into main.

[erezrokah]

I don't think we should add new features to v2. It's in maintenance mode, so only bug-fixes and security-fixes should go in; other changes should go into v3

👍 I wasn't sure what's the timeline for the v3 release. I'll go ahead and close this PR