[Bug]: include mkdock binary in the docker image

[nabuskey]

What is your environment, configuration, and command?

NA

What did you do and What did you see instead?

When enabling the techdoc generation, we get an error message like so:

Building a newer version of this documentation failed. Error: "Failed to generate docs from /tmp/backstage-m3zKfv into /tmp/techdocs-tmp-pXtWRJ; caused by Error: This operation requires Docker. Docker does not appear to be available. Docker.ping() failed with; caused by Error: connect ENOENT /var/run/docker.sock"

This means we need to include the mkdocs-techdocs-core in the docker image like outlined here: https://backstage.io/docs/features/techdocs/getting-started#disabling-docker-in-docker-situation-optional

Additional Information. Logs.

No response