[electrum] add an option to show more verbose output for get_merkle_root

Summary: Add another verbosity level that enables all logs from the electrumabc package. This might help debugging socket issues when running the script on a CI server.

Test Plan:

electrum/scripts/get_merkle_root
electrum/scripts/get_merkle_root -v
electrum/scripts/get_merkle_root -vv
electrum/scripts/get_merkle_root -v -v

contrib/source-control-tools/patch-recipes/update-electrum-checkpoints.sh

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D15356