Reduce the risk of having unregistered metrics

[pracucci]

A mistake, hard to spot during code reviews, is to create Prometheus metrics but not register them to the registry.

In order to overcome this problem, I've drafted a plan in Cortex cortexproject/cortex#2204 long time ago. I did a check and I think we're finally ready to enforce it in Mimir.

My proposed plan is to enforce the usage of promauto.With(reg).XXX() everywhere, doing the following:

• Forbid the usage of prometheus.{MustRegister,Register,DefaultRegisterer} (see Reduce usage of global Prometheus registerer #2750)
• Forbid the usage of promauto.{NewCounter,NewCounterVec,NewCounterFunc,NewGauge,NewGaugeVec,NewGaugeFunc,NewSummary,NewSummaryVec,NewHistogram,NewHistogramVec} and prometheus.{NewCounter,NewCounterVec,NewCounterFunc,NewGauge,NewGaugeVec,NewGaugeFunc,NewSummary,NewSummaryVec,NewHistogram,NewHistogramVec}, except few places where it's very difficult to get rid of it (with a //lint:ignore directive)