[#678] Add Google Tag Manager to the img-src CSP directive

In response to the user story requiring the metadata validation service
to be accessible only from localhost for security reasons, this commit
includes a modification to the CSP (Content Security Policy) directive
in the docker-compose.yml file. The change specifically adds
'https://www.googletagmanager.com' to the img-src directive, ensuring
that resources from Google Tag Manager are permitted in the service.
This adjustment enhances security measures by properly configuring the
CSP policy to allow resources only from specified sources.

scripts/govtool/config/templates/docker-compose.yml.tpl

@@ -250,7 +250,7 @@ services:
       - "traefik.http.routers.frontend.rule=Host(`<DOMAIN>`)"
       - "traefik.http.routers.frontend.entrypoints=websecure"
       - "traefik.http.routers.frontend.tls.certresolver=myresolver"
-      - "traefik.http.middlewares.frontend-csp.headers.contentSecurityPolicy=default-src 'self'; img-src *.usersnap.com 'self' data:; script-src *.usersnap.com 'self' 'unsafe-inline' https://www.googletagmanager.com https://browser.sentry-cdn.com; style-src *.usersnap.com *.googleapis.com 'self' 'unsafe-inline' https://fonts.googleapis.com; connect-src *.usersnap.com https://s3.eu-central-1.amazonaws.com/upload.usersnap.com 'self' o4506155985141760.ingest.sentry.io *.google-analytics.com; font-src *.usersnap.com *.gstatic.com 'self' 'unsafe-inline' https://fonts.gstatic.com; worker-src blob:"
+      - "traefik.http.middlewares.frontend-csp.headers.contentSecurityPolicy=default-src 'self'; img-src *.usersnap.com https://www.googletagmanager.com 'self' data:; script-src *.usersnap.com 'self' 'unsafe-inline' https://www.googletagmanager.com https://browser.sentry-cdn.com; style-src *.usersnap.com *.googleapis.com 'self' 'unsafe-inline' https://fonts.googleapis.com; connect-src *.usersnap.com https://s3.eu-central-1.amazonaws.com/upload.usersnap.com 'self' o4506155985141760.ingest.sentry.io *.google-analytics.com; font-src *.usersnap.com *.gstatic.com 'self' 'unsafe-inline' https://fonts.gstatic.com; worker-src blob:"
       - "traefik.http.routers.frontend.middlewares=frontend-csp@docker"
       - "traefik.http.services.frontend.loadbalancer.server.port=80"