Loosen file name validation for kubernetes service bindings

[tomkennedy513]

Thanks for contributing to cloud_controller_ng. To speed up the process of reviewing your pull request please provide us with:

• A short explanation of the proposed change:

The ServiceBinding spec has been updated to explicitly mention that underscores are valid in credential keys (https://github.com/servicebinding/spec/blob/main/README.md#workload-projection). Updating the implementation to match the change in teh spec

• An explanation of the use cases your change solves

Many service bindings contain underscores in the credential keys. Previously these would return an error even though the spec only stated that credential keys should match the previous regex. The spec was updated to better clarify what should be allowed in credential keys

• Links to any other associated PRs

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[philippthun]

@tomkennedy513 @sethboyles @Gerg @stephanme - As underscores were not valid before, we are transforming several VCAP_SERVICES attributes (e.g. binding_name -> binding-name): https://github.com/cloudfoundry/cloud_controller_ng/blob/a90419c5dcafce9cb209f124e789d255087c5c30/lib/cloud_controller/diego/service_binding_files_builder.rb#L110C11-L112

It would be nice to remove this transformation, although it's an incompatible change. But this feature is marked as experimental, so the question is: shall we dare?

[tomkennedy513]

@tomkennedy513 @sethboyles @Gerg @stephanme - As underscores were not valid before, we are transforming several VCAP_SERVICES attributes (e.g. binding_name -> binding-name): https://github.com/cloudfoundry/cloud_controller_ng/blob/a90419c5dcafce9cb209f124e789d255087c5c30/lib/cloud_controller/diego/service_binding_files_builder.rb#L110C11-L112

It would be nice to remove this transformation, although it's an incompatible change. But this feature is marked as experimental, so the question is: shall we dare?

ya, I left that alone because I wasn't sure if it would be ok to break that. If you think its ok, I'm happy to open another pr.

[stephanme]

@tomkennedy513 : we discussed changing the mapping of the VCAP_SERVICES attributes (currently: underscore to dash) in the ARI WG meeting 26.8.25 and we think it would be good to use the original attribute names. Since the app feature service-binding-k8s is still documented as experimental, we should dare the change (now or never...).

A PR would be very appreciated.

[tomkennedy513]

@tomkennedy513 : we discussed changing the mapping of the VCAP_SERVICES attributes (currently: underscore to dash) in the ARI WG meeting 26.8.25 and we think it would be good to use the original attribute names. Since the app feature service-binding-k8s is still documented as experimental, we should dare the change (now or never...).

A PR would be very appreciated.

@stephanme Here is the pr #4542