create-client: read credentials from a file

Modify `lib/create-client` to read credentials from `$CWD/.auth.json`
first and use ENV variables as an optional overrides.
package: add repository field
Implement `sync-label` bin script.

Add a sync scripts to synchronize all shared labels across all team
projects. The configuration is stored in a file, so that it's easy
to re-run it later.

Add a config file for the loopback/studio team.