Update docs for 0.7

[fmassot]

Fixes:

• Complete the minio config storage with the URI of an index #4285
• Add documentation on local split cache configuration #4334

[trinity-1686a]

we add a bunch of fastfields that we don't need, but can be convenient for our users if they query these index by themselves. We should document the minimum index config that works with Quickwit, so that one can replace the default config with that minimum config, and save on fastfield (and possibly indexing and doc_store) size, if they don't plan on doing anything fancy.

(this is a suggestion for future doc, not a change request for this PR)

[fmassot]

Yes, you are referring to the Jaeger usage. We could add an "optimization" section to put this type of information.