HTTP client issue with libcurl without HTTP/2 support

[SystemKeeper]

• Ref perf(client): enable HTTP/2 and brotli support in internal HTTP client #55433

We implemented HTTP/2 support in the mentioned PR, the PR mentions that we fallback to HTTP/1.1 in case 2 is not support, which for curl is true:

libcurl falls back to HTTP 1.1 if HTTP 2 cannot be negotiated with the HTTPS server.

(https://curl.se/libcurl/c/CURLOPT_HTTP_VERSION.html)

But seems guzzle has a hard check on HTTP/2 support:
https://github.com/guzzle/guzzle/blob/b51ac707cfa420b7bfd4e4d5e510ba8008e822b4/src/Handler/CurlFactory.php#L52-L55

Additionally it seems not be enough to just remove the guzzle option, see nextcloud/talk-android#5887.

I am not sure how big of an issue that is, as I would assume most libcurls currently do support HTTP/2. But maybe we should be more graceful.

[ben-eSM]

That's exactly my issue. I have an older libcurl without the HTTP/2 Support compiled. After the update, Nextcloud is barely usable. Can't connect to the store and most apps are disabled because they can't be updated.

[SystemKeeper]

You can just revert #55433 for now, to put it in a working state again.