Don't limit number of Gitaly client keepalives

Long-running RPCs, such as `ForkRepository`, may take several hours
to complete. While Sidekiq waits for the RPC to complete it should send
keepalive pings to Gitaly/Praefect to prevent load balancers from
killing the connection. However, the default value for
`GRPC_ARG_HTTP2_MAX_PINGS_WITHOUT_DATA` is only 2, with pings
sent at 5 minute
intervals.

As a result, Sidekiq will only send keepalives for the first 5 minutes,
then leave the connection idle for up to 6 hours and putting
long-running RPCs at risk of failure.

This commit sets `GRPC_ARG_HTTP2_MAX_PINGS_WITHOUT_DATA` to 0, so
Sidekiq can send an unlimited number of keepalives and keep long-running
RPCs active. Note that pings are still sent at 5 minute intervals with
this change.

Changelog: fixed

lib/gitlab/gitaly_client.rb

@@ -56,7 +56,8 @@ module Gitlab
       # https://gitlab.com/gitlab-org/gitaly/-/blob/bf9f52bc/client/dial.go#L78
       {
         'grpc.keepalive_time_ms': 20000,
-        'grpc.keepalive_permit_without_calls': 1
+        'grpc.keepalive_permit_without_calls': 1,
+        'grpc.http2.max_pings_without_data': 0
       }
     end
     private_class_method :channel_args