remove URLs from proto description

[craigbox]

https://istio.io/latest/docs/reference/config/networking/destination-rule/#ConnectionPoolSettings-HTTPSettings

Maximum number of requests that will be queued while waiting for a ready connection pool connection. Default 2^32-1. Refer to https://www.envoyproxy.io/docs/envoy/latest/intro/arch_overview/upstream/circuit_breaking under which conditions a new connection is created for HTTP2. Please note that this is applicable to both HTTP/1.1 and HTTP2.

Change these URLs to markdown throughout the refdocs. This will need to be done on the istio/api repo (in master and release-1.24) but as there is not currently any automation to move the refdocs here, it can be done here simultaneously.

(While you're there, standard use of "HTTP/2" instead of "HTTP2".)