Fix use of SSL cert for Docker runner and HTTPS

What does this Merge Request do and why?

Currently a Docker runner gets a 403 when trying to connect a GDK configured to use HTTPS - this is because the SSL certificate is not correctly configured for the runner. This MR fixes that problem by:

• Updating the Procfile template so that when HTTPS is enabled for GDK and the runner executor is Docker, the SSL certificate configured in gdk.yml will be uploaded to the Docker runner container
• Updating the gitlab-runner-config.toml template so that when HTTPS is enabled and the runner executor is Docker, tls-ca-file will not be configured. The template will instead be read from /etc/gitlab-runner/certs in the Docker container

First MR for gitlab#369351 (closed)

Merge Request checklist

• This change is backward compatible. If not, please include steps to communicate to our users.
• Tests added for new functionality. If not, please raise Issue to follow-up.
• Documentation added/updated, if needed.
• gdk doctor test added, if needed.
• Add the ~highlight label if this MR should be included in the CHANGELOG.md.