Add PDS_MANUAL_CERTS env set

[jamesmanes]

NOTE: Second PR on the PDS side to leverage this can be found here: bluesky-social/pds#155

Rationale

PDS administrators may want to leverage caddy for on-demand TLS rather than hack around with nginx or another server.

Approach

With the introduction of a PDS_MANUAL_CERTS env property, PDS administrators can add a comma-separated list of subdomains (e.g., j.manes.xyz, portfolio.manes.xyz, work.manes.xyz).

Example

I own https://manes.xyz. My handle is james.manes.xyz. I used this domain in the past for a personal landing page at https://j.manes.xyz. I want a cert to exist for j.manes.xyz so that I can properly redirect it or proxy-pass it in the caddy config file without having to replace caddy with nginx or apache.

[ledlamp]

What? This makes no sense. Just add your sites to the caddy config and it will get certs.

[jamesmanes]

What? This makes no sense. Just add your sites to the caddy config and it will get certs.

Can you offer an example? Adding sites to the caddy config was not enough for me, as there is a check in the index.js file that excludes subdomains that do not have PDS accounts associated with them.