Improve experience of publishing Features|Templates to Dockerhub

[joshspicer]

Reported in the Dev Container Community Slack (ref).

Dockerhub has a lot of special cases that this CLI's container registry implementation needs to support. One that I noticed is that the key name in the ~/.docker/config.json is "https://index.docker.io/v1/". This CLI currently uses this key to map to the published registry name - all other examples omit https and don't have any additional path (v1). Both of these components will need to be handled when building the URI

This could be lumped into https://github.com/devcontainers/cli/issues/468, as I think this is mostly an auth special case.

Once fixed, add regression testing to https://github.com/devcontainers/cli/blob/main/src/test/container-features/registryCompatibilityOCI.test.ts.