[chronik] Fix a race in chronik_resync.py

Summary:
When doing a full reindex via -reindex, both chronik and the node are reindexing.

The chronik reindex is blocking until it catches up with the node, which will happen on the first block in the case of a full reindex. So before the tip become available we need to wait:

• For the node to be fully synced
• For chronik to drain the validation interface queue

Test Plan:

./test/functional/test_runner.py chronik_resync

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D17244