py-sdk: add register_prefix SDK call

[andrea-reale]

Related

• Closes RR-1962
• Follows:
  • implement registration by prefix: OSS server #11564
  • https://github.com/rerun-io/dataplatform/pull/1864

What

This PR builds up on the previous work and adds a new register_prefix python
SDK function that allows end-users to register all the recordings under a given
object store prefix (i.e., a directory).

Why

In a previous version of this change, we allowed users to register a prefix
simply by implicitly interpreting any trailing '/' in the object store URL as meaning
the customer wanted to register a prefix.

As debated in #11564, however, this is error prone, so we moved to requiring an explicit signal.

Instead of modifying the signature of the existing register_batch function in non-obvious
and possibly odd ways, I decided to add a new function that is explicit in its intent, that is.
register_prefix.

FAQs

• The redap API allows prefix and non-prefix DataSources to be mixed in the same call. Why does
  the python SDK not allow this?
  • We'd need to make the register_batch python function signature more complex and awkward.
    This keeps the user surface simple, while leaving room for future improvements if needed.
• Why not register_prefixes (plural)?
  • We could, but I don't see a strong use case for registering multiple prefixes
    at once.

Testing

Manually

[github-actions]

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Result	Commit	Link	Manifest
✅	7229ee7	https://rerun.io/viewer/pr/11600	+nightly +main

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[abey79]

Apart from the bikeshedding, this lgtm, thanks.

[abey79]

I'm not sure about the signature, see slack thread.