* Add support for obtain ECDSA keys

* Replace matrix_ssl_lets_encrypt_use_ecdsa_keys for matrix_ssl_lets_encrypt_key_type

Playbook is retrieving certificates for some endpoints which were
not listed in the doc

# chain.pem file is required for 'ssl_trusted_certificate`

Fix https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/1073

Fixes #586 (Github Issue)

We had something like that on the Server Delegation how-to page,
but it's better if we have it on the SSL certificates page.

Relocated there and improved linking.

Fixes #94 (Github Issue)

Adds support for managing certificates manually and for
having the playbook generate self-signed certificates for you.

With this, Let's Encrypt usage is no longer required.

Fixes Github issue #50.