[Chronik] Move abort_node and shutdown_requested into ChronikBridge

Summary:
Similar reasoning to D15537, this unblocks potential backports from Core that refactor AbortNode and ShutdownRequested to require NodeContext.

Depends on D15538.

Test Plan: ninja check-functional

Reviewers: Fabien, #bitcoin_abc

Reviewed By: Fabien, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D15539