feat: enable use of CEL expressions for CR valueFrom

[alexandernorth]

What this PR does / why we need it:

Adds CEL (Common Expression Language) support to Custom Resource State metrics for transforming and extracting values from custom resources.

CEL expressions enable more complex calculations, conditional logic, array/object iteration, and dynamic label generation directly in metric configurations, with a low cost overhead. This is more flexible than the existing path-based approach for complex data structures (multi-level, iteration, etc).

Examples:

Static number:

valueFrom:
  celExpr: "1.0"

Iterate over arrays adding dynamic labels:

valueFrom:
  celExpr: "value.map(c, WithLabels(c.status, {'type': c.type}))"

Path-based valueFrom continues to work unchanged for backwards compatibility.

The documentation is also updated to include examples and details on the implementation customresourcestate-metrics.md

How does this change affect the cardinality of KSM: (increases, decreases or does not change cardinality)
None.

Which issue(s) this PR fixes: (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged)
I did not find a specific comment, but it does solve a TODO regarding multi-length valueFrom paths: #1958 (comment)

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