[land-bot] Call land-patch when generating automated commits

Summary:
This decouples generation of automated commits from the landing logic.
land-patch.sh can be used to land the change generated from this script, so there
is no need to duplicate this logic here.

Depends on D7467

Test Plan:

COMMIT_TYPE=archive-release-notes ./automated-commits.sh -p HEAD

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Subscribers: Fabien, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D7476