follow-ups for compare-and-swap in governor

Summary

• fix: add instance id to cas predicate when changing replicaset's target master

Strictness!

• fix: move automatic cas-predicate construction to the server side

• refactor: Predicate::check_entry -> check_predicate

• fix: retry "not a leader" errors when self-activating on startup

• fix: picodata expel calls proc_expel_redirect

• fix: make sure local compare-and-swap requests are never redirected

• fix: don't block the event loop in pico.raft_log()

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• Close #785 (closed)
• Relates to #856 (closed)
• Follow-up for !1254 (merged)
• Cherry-pick to: none
• Docs follow-up: proc_cas behaviour: if predicate has empty ranges, they'll be auto-generated based on the raft operation. Spefically if it's a dml the ranges will just check for equality with the primary key of the operations