Create Dockerfile for ansible+dotgpg use

It would be useful to have a "clean" container-based system which can perform the adoptium sysadmin operations without requiring tools to be installed on people's own machines. This should include:

1. A version of ansible that will work for our systems
2. Appropriate ssh configuration if necessary (e.g. for connecting to Solaris machines)
3. A usable `dotgpg` install

Once this is created, basic instructions should be written to make the use of this as simple as possible.

No file or test is identified in the issue, so start by reviewing the repository's existing Ansible setup and any current operator instructions. Done means providing a container with a compatible Ansible version, any required SSH configuration, and a usable dotgpg installation, plus basic instructions for running it.

Written by the indexing model from the issue text.