feat: hook builder options for dimension extraction

[Kavindu-Dodan]

This PR

Fixes #381

Adds callback option to extract custom dimensions from flag evaluation metadata.

This is similar to what we do in JS SDK - open-feature/js-sdk-contrib#520

MetricHookOptions hookOptions = MetricHookOptions.builder()
        //Configure a callback which accepts ImmutableMetadata
        .attributeSetter(metadata -> Attributes.builder()
            .put("boolean", metadata.getBoolean("boolean"))
            .put("integer", metadata.getInteger("integer"))
            .build())
        .build();

This change is backward compatible and does not change the current beavhior.