Abstract out BlockAssembler options

Summary:
This is a partial backport of Core PR9868

It was modified as to extract the required infos from the config and only use the option object going forward, which avoid having two source of truth.

Test Plan:

make check
./test/functional/test_runner.py --extended

Reviewers: #bitcoin_abc, jasonbcox

Reviewed By: #bitcoin_abc, jasonbcox

Subscribers: Fabien, jasonbcox

Differential Revision: https://reviews.bitcoinabc.org/D4072