add docker labels for dependabot

[qrkourier]

This is to configure Dependabot to bump the source image version of ziti-console in the Dockerfile for ziti-controller.

refs:

• https://github.com/openziti/ziti/blob/release-next/.github/dependabot.yml#L41
• https://github.com/openziti/ziti/blob/release-next/dist/docker-images/ziti-controller/Dockerfile#L8
• https://docs.github.com/en/code-security/dependabot/dependabot-version-updates/configuration-options-for-the-dependabot.yml-file?learn=dependency_version_updates&learnProduct=code-security#docker