We should remove Caddy from the workerised Complement container image, because it's confusing having both Nginx and Caddy

[reivilibre]

Our current Complement-with-workers image uses Nginx to route worker requests to the right worker and uses Caddy to do TLS termination.

Whilst it's convenient that Caddy can generate the TLS certificate on-demand (I guess), it's frustrating that it's configured with a very messy and under-documented JSON file.
It's also confusing that we use two reverse-proxies in the same image.

Nginx can terminate TLS just fine and a handful of OpenSSL commands can generate a certificate (this is what the non-workerised version does), so I think it'd be cleaner to get rid of Caddy from the 'architecture' of our worker image.