feat: Define Docker image

[microamp]

Creating a new image for Trustee as per @NGPixel's suggestion earlier.

I think it would be preferrable to create a docker image that inherits the legacy-base one and adds the apache config change, as it's not private data and it makes 1 less manual thing to take care of should a redeploy be needed (and it avoids mounting a volume just for 1 config file).

(Update: The repo has been renamed.)

I noticed that /etc/apache2/sites-enabled/000-default.conf is just a symlink of /etc/apache2/sites-available/000-default.conf, so I'm updating the actual file rather than the symlink here.

The repo is currently private but can be mad public once this PR is merged. (The repo will remain private for now. See comments below.) Feel free to make any necessary changes.

[rjsparks]

It should not be made public with this name. The trustees doesn't consider themselves, or their website legacy, and it would attract an unnecessary discussion with the trust explaining its purpose. I suggest something like 'trustee-proxyenv'

[rjsparks]

Also remember when naming anything that might become public (and note that it's hard to guess what might) to follow the guidance at https://datatracker.ietf.org/doc/statement-iesg-iesg-statement-on-inclusive-language-20210511/

[microamp]

@rjsparks Thanks for your comments. Understood. I have renamed the repo, and replaced all occurrences of the old name with the new one.

Update: I'll make the repo public based on the conversation I had with the team earlier.