plugin app manager: various improvements: - Generated password must now be named and are stored, so they are re-used on following restarts. Password size can now be specified. - New `not` filter for `!libervia_param` to inverse a boolean value. - Former `front_url` field has been renamed to `web_url_path` as it is the URL path used for web frontend. All Web frontend related field are prefixed with `web_`. - `front_url` is now used to specify a whole front URL (notably useful if an app uses its own domain). A list can be used to retrieve a key, like for `url_prefix`, and `https` scheme is added if no scheme is specified. - An abstract class is now used for App Managers. - Last application start time is stored in persistent data.

Those certificates are used to activate TLS for end-2-end testing (to be as
close as possible as production environment), they are used in other containers
needing TLS certificates (notably Prosody).

To generate them, minica has been used. Minica can be found at https://github.com/jsha/minica.

The following commands have been used:

$ minica --domains "server1.test,*.server1.test,server2.test,server3.test,libervia-backend.test,libervia-web.test"
$ chmod 0644 minica.pem server1.test/cert.pem && chmod 0640 server1.test/key.pem

Note that certificates are valid for 2 years and 30 days, so they must be renewed after this delay.