Allow --link name to start with a number

[scsmithr]

It would be nice to run docker run -it codercom/code-server:latest --link and not have to specify an argument to link. However this will fail most of the time with Name must conform to regex ^[a-z][a-z0-9_]{0,50}$ because --link defaults to host name (I think), and docker host names start with a number more often than they start with a letter.

[nhooyr]

cc @sreya

[nhooyr]

We can strip leading numbers before passing to the cloud agent but I agree, I don't see a good reason why leading numbers shouldn't be allowed.

[sreya]

This has already been fixed server-side, should be fixed in the next release for code-server

[nhooyr]

Awesome!

[nhooyr]

Marking this as fixed then, just need to mention it in the release notes.