Update module yaml to v2.4.0

See merge request !4

Configure Renovate

See merge request !2

This is useful for, e.g. OCSP stapling.

Switch to certbot pem names

See merge request ai3/tools/acmeserver!1

Easier to swap between the two.

Support multiple config_dirs, name all paths explicitly instead of
simply using predefined subdirectories.

Add dns-01 support, make the code more readable, add a testing
mode that will generate self-signed certificates (for test
environments that are not reachable from outside).