Make config version available on client at runtime

This is a feature request. The response from the config server when a client requests its config contains a version. It would be nice if this version were available at runtime on the client so you can check what specific version of config is being used by a client at a given time. While the label is known on the client, it could be a git branch which points to different commits at different times.

A couple off the cuff ideas:
An InfoContributor that adds this information to the /info Actuator endpoint. Another idea is incorporating this version into the /env Actuator endpoint, perhaps most simply by naming the property sources with the version. It might be nice to somehow separately know the environment repositories contributing to the environment and their version, considering there may be more than one (tangentially related: the version is always null in the config server response when using the composite env repo).

Start by tracing how the config client receives the config server response and how the /info and /env Actuator endpoints expose runtime data. Compare the proposed InfoContributor and property-source naming approaches, including composite environment repositories. Done means the config version or contributing repository versions are available on the client at runtime.