observability: add grafana graphs/alerts for failure checks and watcher

[luketchang]

• [ ] Add grafana display for the number of double updates a watcher has observed (fine if 0, go crazy with alerts if >= 1)

• [ ] Add grafana graph for number of updates the watcher has inspected for double updates (should be up and to the right if watcher is functioning properly)

• [ ] Add grafana display for number of times home has been observed as failed (fine if 0, go crazy with alerts if >= 1)

• [ ] Add grafana graph for number of home failure checks an agent has performed (should be up and to the right if agent is healthy)

[luketchang]

cc @arnaud036 @yourbuddyconner