Add pre-push (#977)

* Add pre-push git hook
* Don't run docker-compose in pre-push git-hook

Not all contributors use docker-compose.

* Setting FD limit to 4096 if possible, shellcheck reports lint issue SC2039 due to "ulimit -n" being undefined under POSIX
* Capped FD limit at 4096

In production, the limit is 8096. This is a canary that notices if docs.rs is using too many file descriptors locally and lets the team fix the outage before it affects production.

Author: ohaddahan

.git_hooks/pre-push

@@ -0,0 +1,17 @@
+#!/usr/bin/env sh
+fd_hard_limit="$(ulimit -n -H)"
+if [ "$fd_hard_limit" = "unlimited" ] || [ "$fd_hard_limit" -ge 4096 ] ; then
+  ulimit -n 4096
+else
+  ulimit -n "$fd_hard_limit"
+fi
+
+if ! cargo test ; then
+  printf "\n"
+  printf "\033[0;31mpre-push hook failed during:\033[0m\n"
+  printf "\033[0;31m\tcargo test\033[0m\n"
+  exit 1
+fi
+
+printf "\n"
+printf "\033[0;32mpre-push hook succeeded\033[0m\n"