support "True" and "False" as string in custom-resource-state

[jabdoa2]

What this PR does / why we need it:
Kubernetes Operators usually store status conditions in the following format:

status:
  conditions:
    - lastTransitionTime: "2019-10-22T16:29:31Z"
      status: "True"
      type: Ready

Note that status is actually a string. This previously broke KSM custom-resource-state gauges because it could not convert strings to float. This PR maps "True", "true", "Yes" and "yes" to 1.0 and "False", "false", "No", "no" to 0.0. This allows us to use custom-resource-state for all CRD objects of standard kubernetes operators.

For a single condition you can use (as in unit test status_conditions):

      - --custom-resource-state-config
      # in YAML files, | allows a multi-line string to be passed as a flag value
      # see https://yaml-multiline.info
      -  |
          spec:
            resources:
            - groupVersionKind:
                group: xxxxx.xxx
                kind: "xxx"
                version: "v1"
              metrics:
              - name: "xxx_ready"
                help: "xxx ready state"
                each:
                  type: Gauge
                  gauge:
                    path: [status, conditions, "[type=Ready]", status]

To expose one metric per status type (as in unit test status_conditions_all):

      - --custom-resource-state-config
      # in YAML files, | allows a multi-line string to be passed as a flag value
      # see https://yaml-multiline.info
      -  |
          spec:
            resources:
            - groupVersionKind:
                group: xxxxx.xxx
                kind: "xxx"
                version: "v1"
              metrics:
              - name: "xxx_status"
                help: "xxx status"
                each:
                  type: Gauge
                  gauge:
                    path: [status, conditions]
                    labelsFromPath:
                      type: ["type"]
                    valueFrom: ["status"]

Guess this could be something for the documentation as it will be a very common usecase for controller CRDs.

How does this change affect the cardinality of KSM: (increases, decreases or does not change cardinality)
It does not change cardinality. It allows KSM to support .status.conditions used by standard kubernetes operators.

Which issue(s) this PR fixes
Fixes #1962

[linux-foundation-easycla]

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[mrueg]

Since this really depends on the implementor of the CR, having some defaults make sense. Anything else really should be defined via a user supplied valuemap (e.g.if the implementation returns "Ok" etc.).

[mrueg]

/approve

[mrueg]

It would be good to add a sentence or two to https://github.com/kubernetes/kube-state-metrics/blob/main/docs/customresourcestate-metrics.md about this conversion.

[rexagod]

/approve

[logicalhan]

/assign
/triage accepted

[dgrisonnet]

/approve
/lgtm

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This pull-request has been approved by: dgrisonnet, jabdoa2, mrueg, rexagod

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