refactor: move all shellcheck disable definitions to .shellcheckrc file

This makes standard use of shellcheck work without needing to provide extra configuration anywhere.

Also remove use of inline 'shellcheck disable' calls that are already defined in the .shellcheckrc and don't need to be set inline.

plugins/20_events/install

@@ -14,7 +14,6 @@ trigger-events-install() {
 
   # This can be done unconditionally as mkdir -p
   # exits gracefully if the path already exists
-  # shellcheck disable=SC2174
   mkdir -m 775 -p "$DOKKU_LOGS_DIR"
   case "$DOKKU_DISTRO" in
     arch | debian | raspbian)