Add shellcheck to web, server-pro, server-ce (#23823)

* Update shellcheck files to include non ".sh" files having the sh shebang

* Add shellcheck to root Makefile

* `make shellcheck_fix`

* Add shellcheck to server-ce and server-pro

* Exclude SC1091 (Not following) in SP/CE

* Fix errors in SP

* Fix errors in CE

* Update root shellcheck to ignore all failing rules. We can later remove rules one by one.

* Add shellcheck to web

* Add shellcheck step for server-ce and server-pro in cloudbuild.yaml

* Revert "Add shellcheck to root Makefile"

This reverts commit e0fa56f2

* Revert "`make shellcheck_fix`"

This reverts commit eb179245c109a9e742a7fdeeb75a4bdd03963587.

* `make shellcheck_fix` in server-ce

* Fix: Use $(...) notation instead of legacy backticked

```
In init_scripts/100_set_docker_host_ipaddress.sh line 5:
echo "`route -n | awk '/UG[ \t]/{print $2}'` dockerhost" >> /etc/hosts
      ^-- SC2006 (style): Use $(...) notation instead of legacy backticks `...`.

Did you mean:
echo "$(route -n | awk '/UG[ \t]/{print $2}') dockerhost" >> /etc/hosts

For more information:
  https://www.shellcheck.net/wiki/SC2006 -- Use $(...) notation instead of le...
```

* `make shellcheck_fix` in web

* Manual corrections on autofix

* Update SHELLCHECK_FILES to Perl regex so it matches at start of file

GitOrigin-RevId: 815d53f319a3792efa22703beb75570de5977450

server-ce/init_scripts/100_set_docker_host_ipaddress.sh

@@ -2,4 +2,4 @@
 set -e -o pipefail
 
 # See the bottom of http://stackoverflow.com/questions/24319662/from-inside-of-a-docker-container-how-do-i-connect-to-the-localhost-of-the-mach
-echo "`route -n | awk '/UG[ \t]/{print $2}'` dockerhost" >> /etc/hosts
+echo "$(route -n | awk '/UG[ \t]/{print $2}') dockerhost" >> /etc/hosts

server-ce/init_scripts/200_nginx_config_template.sh

@@ -26,6 +26,7 @@ if [ -f "${nginx_template_file}" ]; then
   # Note the single-quotes, they are important.
   # This is a pass-list of env-vars that envsubst
   # should operate on.
+  # shellcheck disable=SC2016
   envsubst '
     ${NGINX_KEEPALIVE_TIMEOUT}
     ${NGINX_WORKER_CONNECTIONS}