Using Spring SPEL in the @Observed annotation to allow dynamic low and high cardinality values

[mloayzagahona]

Please describe the feature request.
Using Spring SPEL in the @Observation annotation to allow dynamic low and high cardinality values

Rationale
Use Spel expression in the @Observed annotation to allow dynamic values for the low cardinality

@Observed(
      name = "observed-feature",
      contextualName = "context-one",
      lowCardinalityKeyValues = {"action", **"#method1"**})
public ResponseEntity<Object> doPost(String method1, HttpHeaders header)

Additional context
When using low cardinality in the observation, it adds to the metric as tag, and I'm looking to add tags dynamically to the underlying created metric for this observation.

[shakuzen]

Micrometer does not depend on Spring and we cannot (it would create a circular dependency because Spring in turn depends on Micrometer). For that reason, we cannot directly support Spring Expression Language. We do however have @MeterTag which can be configured to use a ValueExpressionResolver implementation that understands SpEL. That won't currently work with the @Observed annotation, though. I thought we had another issue for that, but I couldn't find one when searching now. We can change this issue to be an enhancement request for that, however, if it sounds like it would allow what you want.

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