[Chronik] Add -chronikreindex to only reindex Chronik

Summary:
Many such cases where it's necessary to leave the rest of the node untouched and only reindex Chronik.

Depends on D13315.

Test Plan: ninja && ./test/functional/test_runner.py chronik_reindex

Reviewers: Fabien, #bitcoin_abc

Reviewed By: Fabien, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D13320