Health indicators for vector stores (and any other external APIs)

[habuma]

Given that vector stores are databases that are external to the application, which could go down or otherwise become unavailable, and as such contribute to the health (or lack thereof) of a Spring AI application...

It would be great if Spring AI provided health indicators for the vector stores that contribute to Actuator's health endpoint.

One question concerning this is whether such health indicators would be needed for vector stores that are also databases for which Spring already has health indicators. For example, Postgres and Mongo probably are already covered by health indicators. But things like Chroma and Milvus probably aren't.

[eddumelendez]

I started this some time ago and shared it with @markpollack and @tzolov at Spring IO but never raised the PR. Currently, it is missing some tests. I can start raising a draft PR to start discussing about it.