BRP System Ordering

[mnmaita]

Objective

• Attempts to fix System ordering around BRP (Bevy Remote Protocol) #16042

Solution

• Added a new RemoteSystem SystemSet for the BRP systems.
• Changed the schedule on which these systems run from Update to Last.

Testing

• I did not test these changes and would appreciate a hand in doing so. I assume it would be good to test that you can order against these systems easily now.

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Migration Guide

• process_remote_requests, process_ongoing_watching_requests and remove_closed_watching_requests now run in the Last schedule. Make sure you use RemoteSystem SystemSet in case you need to order your systems against them.

[MiniaczQ]

I mentioned it in the issue, but I'd consider adding a custom schedule for this, to ensure BRP-unaware users don't mix their systems with BRP systems.
In that case a system set seems pretty unnecessary, at least for the current system complexity

[mockersf]

No preference from me between Last or its own schedule, both seems fine to me