Allow dashes/hyphens in devtainer names

Dashes/hyphens (but not sucessive dashes/hyphens) are now allowed in devtainer names. This means you can now name a devtainer my-devtainer rather than mydevtainer.

Upgrade to this version should be safe for most users as the URLs for accessing existing devtainers has not changed.

However, upgrade may not be safe where you are using existing devtainers, launched from a Dockside image, for developing Dockside within Dockside. The outcomes in this case are not clearly defined and your access to devtainers launched 'inside' an inner Dockside development devtainer may fail, as the domains will have changed (e.g. from ide-innermost-innerdockside... to ide-innermost--innerdockside. If you are developing Dockside in Dockside, we strongly recommend you commit all WIP to branches before deleting and relaunching your Dockside development devtainers from a newsnowlabs/dockside:latest image.