[repo-pull] Support curl hook

This commit adds a CURL command hook. This enables the Gerrit REST API
access through other authentication mechanisms.

Bug: b/269362063
Test: Run gerrit.py, repo_patch.py, repo_review.py with --use-curl=curl
Change-Id: I6dc4eb78760ee598df5065665c15d689916706f0
5 files changed