feat(metrics) add links to grafana from instance detail page

[edlerd]

Done

• add grafana base url to the settings
• add links to grafana from instance detail page if its base url is configured

QA

1. Run the LXD-UI:
   • On the demo server via the link posted by @webteam-app below. This is only available for PRs created by collaborators of the repo. Ask @mas-who or @edlerd for access.
   • With a local copy of this branch, build and run as described in the docs.
2. Perform the following QA steps:
   • setup o11y stack for lxd
   • configure grafana base url
   • test the links

todo: allow deep links to rows in dashboards, see grafana/grafana#82827

[webteam-app]

Demo

Jenkins

demos.haus