Use of outdated bootstrap library

[swestcott]

During a routine security test it was found that Prometheus is using Bootstrap 3.3.1 which has a known XSS issue (twbs/bootstrap#20184). Further to this Bootstrap 3 is no longer maintained.

Environment

• Prometheus version: 1.7.2, but confirmed in master also (https://github.com/prometheus/prometheus/blob/master/web/ui/templates/_base.html#L8)

[brian-brazil]

From a look at our code, we're not using this anywhere. All the places where we've untrusted data we're handling with Go templating's escaping.

[simonpasquier]

Closed by #5226