Set Monolith opcode enable script flag if monolith enabled

Summary:
Sets the SCRIPT_ENABLE_OPCODE_MONOLITH flag if monolith has been enabled

Co-authored-by: Joshua Yabut <yabut.joshua@gmail.com>
Co-authored-by: Marcos Mayorga <mm@mm-studios.com>
Co-authored-by: Daniel Connolly <daniel@dconnolly.com>

Test Plan:
  make check

Added an integration test for activation.

Reviewers: #bitcoin_abc, jasonbcox

Reviewed By: #bitcoin_abc, jasonbcox

Subscribers: jasonbcox, teamcity

Maniphest Tasks: T299

Differential Revision: https://reviews.bitcoinabc.org/D1231