[CI] Automatically update the AUR package version

Summary:
This diff adds 2 new targets to the automated commits to bump the AUR
packages version according to the current node software version. It is
designed to run continuously and prevent from downgrades.

Depends on D7360.

Test Plan:

COMMIT_TYPE=update-aur-version-bitcoin-abc \
  ../contrib/source-control-tools/automated-commits.sh -p master

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D7361