Add a max_streams option to the *https* plugin to limit the number of
concurrent HTTP/2 streams per DoH connection. This lets operators cap
per-connection concurrency (guarding against resource exhaustion) or
raise it above the Go default for high-fan-in clients that multiplex
many requests over a single connection.
Semantics match the existing *https3* plugin's max_streams:
- omitted -> Go HTTP/2 server default is used
- 0 -> use the underlying HTTP/2 transport default
- positive -> advertise exactly that many concurrent streams
- negative -> rejected at config parse time
The limit is applied via the standard library http.Server.HTTP2
(HTTP2Config.MaxConcurrentStreams) so it is advertised in the server's
SETTINGS frame.
Signed-off-by: Mekias Yohannes <mmyohannes@gmail.com>
2b8c305203