ENABLE_STARTTLS is designed to replace ENABLE_STARTTLS_AUTO by accepting
three values: 'auto' (the default), 'always', and 'never'. If
ENABLE_STARTTLS isn't provided, we fall back to ENABLE_STARTTLS_AUTO. In
this way, this change should be fully backwards compatible.

Resolves #20311

* Format JSON and YAML using Prettier

* Add prettier to devDep

* Change references to tootsuite/mastodon to mastodon/mastodon

* Remove obsolete test fixture

* Replace occurrences of tootsuite/mastodon with mastodon/mastodon in CHANGELOG

And a few other places

* Add ffmpeg buildpack for scalingo.

* Add environment variable to install ffprobe

Note: For existing applications, admins needs to add 'WITH_FFPROBE=true' to environment variable.

* Allow SMTP auth method customization

* Add SMTP openssl_verify_mode option support

Allows one use self-signed certs with their SMTP server.

* Add SMTP enable_starttls_auto option support

Allows the user to set the address mastodon emails are maraked as being sent from