forwardPorts should also allow "." (dot) in the service name

In our usecase, we name the services like `dev.localdev` and `db.localdev` in order to be able to use a `no_proxy` on `.localdev`.
That means that forwarding a port from a service other than the dev-container would look like: `db.localdev:5432` which works perfectly fine when manually adding that port with vscode.
But defining that in the `devcontainer.json` fails because the regex only covers `[a-z0-9-]`.
In my opinion, the regex could be extended to also allow `.`, so `[a-z0-9-\.]`.