Build: Introduce shellcheck (#18081)

* Build: introduce shellcheck

Fixes #16198

scripts/trigger_docker_build.sh

@@ -1,9 +1,9 @@
-  #!/bin/bash
+#!/bin/bash
 
 _circle_token=$1
 _grafana_version=$2
 
-trigger_build_url=https://circleci.com/api/v1/project/grafana/grafana-docker/tree/master?circle-token=${_circle_token}
+trigger_build_url="https://circleci.com/api/v1/project/grafana/grafana-docker/tree/master?circle-token=${_circle_token}"
 
 post_data=$(cat <<EOF
 {
@@ -14,10 +14,10 @@ post_data=$(cat <<EOF
 EOF
 )
 
-echo ${post_data}
+echo "${post_data}"
 
 curl \
 --header "Accept: application/json" \
 --header "Content-Type: application/json" \
 --data "${post_data}" \
---request POST ${trigger_build_url}
+--request POST "${trigger_build_url}"