cli.db: Open init-admin subcmd to initialize superuser-level scripts
In staging, the db is already created by puppet (with necessary users, etc...).
The current create database cli swh db create
does not work currently. The
subsequent steps of postgresql extensions installation is required though (and
it's currently stuck on the creation step failing).
This commit allows to use the init-admin to just install those extensions (and eventually add/update existing/new ones).
In future diffs, we could also fallback to the postgresql image ability to
create the database during its initialization (and then drop the current if db exists
instruction in our entrypoint scripts). D4377 demonstrates such a
behavior \o/
Related to swh/infra/sysadm-environment#2736 (closed)
Test Plan
current tox is happy
(I'll investigate later on how properly test those cli #2741 (closed) -> !184 (closed)).
Migrated from D4374 (view on Phabricator)