Add update-manpages to automated-commits

Summary:
This enables us to automatically update manpages immediately prior to cutting a release.

Depends on D5248

Test Plan:

COMMIT_TYPE=update-manpages ./automated-commits.sh

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D5330