Add Options for MetricValidator

[kristinapathak]

bascule/basculechecks/metrics.go

Line 104 in d160adf

}, ServerLabel, OutcomeLabel, ReasonLabel, ClientIDLabel, PartnerIDLabel, EndpointLabel),

Some Option ideas:

• WithEndpoints([]*regexp.Regexp) - if not provided, an empty string (would cause CapabilitiesMap to error out every time; not ideal) or n/a could be used instead of not_recognized. Then someone testing would be able to determine if the label value is a configuration/setup issue. This could also be providing a function that determines the endpoint label to use given the url in the request.
• MonitorOnly() - errorOut should be true by default. If this option is provided, it will be false.

An added benefit of having a NewMetricValidator function is it allows us to nil check the measures and CapabilitiesChecker.

[joe94]

Sounds good to me 👍
The part about a default label value for endpoints reminded me that we could improve readability in this function by having it return a struct with the different label values as fields.

bascule/basculechecks/metricvalidator.go

Line 118 in d160adf

func (m MetricValidator) prepMetrics(auth bascule.Authentication) (string, string, string, string, error) {

This could be part of this issue or be on its own.