Feign Metrics not exposed in AOT mode via `MicrometerCapability`

[dpozinen]

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Now, I realise that the issue isn't actually in SC open feign, and feign doesn't officially support AOT, but nevertheless there is a FeignHints registrar, so i think it won't hurt extending it.

I suspect that Capability-s in general don't work in native at all for two reasons:

• The way capabilities are registered/enriched via reflection (using method names and return types). This can be fixed by adding hints for MicrometerCapability and other default ones.
• The way enrich-able fields are collected by scanning Builders. This can be fixed by adding hints for BaseBuilder and its child classes.

Unfortunately, I don't have the time to make a proper contribution with tests etc. Thanks in advance