Adds a pediodic job to sync tenants with chatops-proxy. Register request
will behave as upsert, allowing us to backfill new tenant's columns:
stack_id and stack_slug. Upsert is not merged on chatops-proxy, so
that's why task handling 409 status on /tenants/register request.
On top of that, I did small refactoring and introduced a new
register_oncall_tenant func, which receives org as an argument to not to
write `register_tenant(org.uuid, org.stack_id, org.stack_slug,.....)`
every time.
Part of https://github.com/grafana/oncall-gateway/issues/247
Need to be merged after https://github.com/grafana/oncall/pull/4559.
48b7eca26d