* add http2 ping checks
* fix test issue
* add h2ping check to config resources
* add new test and docs for h2ping
* fix grammatical inconsistency in H2PING documentation
* resolve rebase conflicts, add test for h2ping tls verification failure
* api documentation for h2ping
* update test config data with H2PING
* add H2PING to protocol buffers and update changelog
* fix typo in changelog entry
Some TLS servers require SNI, but the Golang HTTP client doesn't
include it in the ClientHello when connecting to an IP address. This
change adds a new TLSServerName field to health check definitions to
optionally set it. This fixes#9473.
R.B. Boyer