feat: implement exists and linked subcommands

README.md

@@ -29,11 +29,13 @@ postgres:connect <name>           Connect via psql to a postgres service
 postgres:create <name>            Create a postgres service with environment variables
 postgres:destroy <name>           Delete the service, delete the data and stop its container if there are no links left
 postgres:enter <name> [command]   Enter or run a command in a running postgres service container
+postgres:exists <service>         Check if the postgres service exists
 postgres:export <name> > <file>   Export a dump of the postgres service database
 postgres:expose <name> [port]     Expose a postgres service on custom port if provided (random port otherwise)
 postgres:import <name> < <file>   Import a dump into the postgres service database
 postgres:info <name>              Print the connection information
 postgres:link <name> <app>        Link the postgres service to the app
+postgres:linked <name> <app>      Check if the postgres service is linked to an app
 postgres:list                     List all postgres services
 postgres:logs <name> [-t]         Print the most recent log(s) for this service
 postgres:promote <name> <app>     Promote service <name> as DATABASE_URL in <app>