Reconsider parked chains when enough works piles up

Summary: This add a mechanism that will automatically park deep reorg and reconsider them only if enough work piles up.

Test Plan: Added integration test for the new behavior.

Reviewers: #bitcoin_abc, jasonbcox, Fabien

Reviewed By: #bitcoin_abc, jasonbcox, Fabien

Subscribers: Fabien, schancel, jasonbcox

Differential Revision: https://reviews.bitcoinabc.org/D2004