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.

dokku

@@ -4,7 +4,6 @@ shopt -s nullglob
 
 export DOCKER_BIN=docker
 if [[ -r /etc/default/dokku ]]; then
-  # shellcheck disable=SC1091
   source /etc/default/dokku
 fi
 
@@ -31,7 +30,6 @@ fi
 export DOKKU_HOST_ROOT=${DOKKU_HOST_ROOT:=$DOKKU_ROOT}
 
 export DOKKU_DISTRO
-# shellcheck disable=SC1091
 DOKKU_DISTRO=$(
   . /etc/os-release >/dev/null 2>&1 || true
   echo "$ID"
@@ -109,12 +107,10 @@ fi
 if [[ -n "$SSH_ORIGINAL_COMMAND" ]]; then
   export -n SSH_ORIGINAL_COMMAND
   if [[ $1 =~ config-* ]] || [[ $1 =~ docker-options* ]]; then
-    # shellcheck disable=SC2086
     xargs $0 <<<$SSH_ORIGINAL_COMMAND
     exit $?
   else
     set -f
-    # shellcheck disable=SC2086
     $0 $SSH_ORIGINAL_COMMAND
     set +f
     exit $?