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

[Roemer]

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-\.].