This commit adds a 'matrix-ntfy' role that runs Ntfy server in Docker with
simple configuration, and plumbing to add the role to the playbook.

TODO: documentation, self-check, database persistence.

`localhost` may resolve to `::1` on some IPv6-enabled systems, which will
not work, because we only potentially expose container ports on
`127.0.0.1` when nginx is disabled (`matrix_nginx_proxy_enabled: false`),
not on `::1`.

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/1914

fixes spantaleev/matrix-docker-ansible-deploy#1889

Support for arm64 images tracked in jitsi/docker-jitsi-meet#1214 and added in jitsi/docker-jitsi-meet#1269

Improvement to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/1909

Overlooked in https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/1909

Co-authored-by: ThellraAK <ThellraAK@pop-os.localdomain>
Co-authored-by: Slavi Pantaleev <slavi@devture.com>

Related to 123a45bb21

Provoked by https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/1879

Not sure how bot-sdk's logging level can be adjusted. Seems like
Dimension now hardcodes `LogService.setLevel(LogLevel.DEBUG);` in its
startup code.

Thanks to Julian for pointing this out

Fixup for https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/1899

Co-authored-by: Slavi Pantaleev <slavi@devture.com>

> Error:   19:3      error    wrong indentation: expected 4 but found 2  (indentation)

Fixup for ba51997f7b

We redefine these variables in `group_vars/matrix_servers`, but it's better
to have some defaults in the role as well.