Resolve "Prometheus graphs have no empty state when no data is present"

Closes #42558

See merge request gitlab-org/gitlab-ce!17759

But first, rewrite the performance bar in Vue:

1. Remove the peek-host gem and replace it with existing code. This also allows
   us to include the host in the JSON response, rather than in the page HTML.
2. Leave the line profiler parts as here-be-dragons: nicer would be a separate
   endpoint for these, so we could use them on Ajax requests too.
3. The performance bar is too fiddly to rewrite right now, so apply the same
   logic to that.

Then, add features! All requests made through Axios are able to be tracked. To
keep a lid on memory usage, only the first two requests for a given URL are
tracked, though. Each request that's tracked has the same data as the initial
page load, with the exception of the performance bar and the line profiler, as
explained above.

Move UnresolvedDiscussions vue component

See merge request gitlab-org/gitlab-ce!17538

Fix styling of multiple environments in merge request widget

Closes #40610

See merge request gitlab-org/gitlab-ce!17663

removed pointless test & changed some deployment tests to make more sense
added in v-tooltip

[ci skip]