Add postgresql-client to postgresql-client feature

[duduribeiro]

Currently when you generate an App with postgres and access the devcontainer, it fails to run bin/rails db inside the container terminal because there is no psql installed on it. This commit installs postgresql-client so it can be used inside the devcontainer.

Before installing postgresql-client:

vscode ➜ /workspaces/demo_devcontainer (main) $ bin/rails db
Couldn't find database client: psql. Check your $PATH and try again.

after

vscode ➜ /workspaces/demo_devcontainer (main) $ bin/rails db
Password for user postgres: 
psql (15.6 (Debian 15.6-0+deb12u1), server 15.1 (Debian 15.1-1.pgdg110+1))
Type "help" for help.

demo_devcontainer_development=# 

does it make sense to install postgresql-client on the feature?

Thanks