Add the matrix fqdn and localhost to ntfy's exemption list.
Also allow all ntfy rate limits to be configured through Ansible
variables.

This caused push notifications to be delivered more than once
if multiple `pusher` workers were enabled.

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/2228

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/2228

This fixes a regression since the change done in c1c152f7ac.
When another role (say `matrix-jitsi`) included `roles/custom/matrix-base/tasks/util/ensure_openssl_installed.yml`,
which then included `{{ role_path }}/tasks/util/ensure_openssl_installed_DISTRO.yml`,
that `role_path` variable would end up being the parent role
(`matrix-jitsi`) and not the `matrix-base` role, so we'd get a failure.

An alternative solution may have been to avoid using `role_path`, but
importing roles properly (like we've done in this patch) sounds like a better way.

Unfortunately, `import_role` fails if `tasks_from` is something like
`util/ensure_openssl_installed` (containing a `/`), so I had to move
these utils out of `util/`.

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/2228

This avoids Ansible trying to ensure `community.general.pacman` is
available, even if that module will never run (because `when` says so).

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/2228

- https://github.com/matrix-org/dendrite/releases/tag/v0.10.7

This paves the way for installing other roles into `roles/galaxy` using `ansible-galaxy`,
similar to how it's done in:

- https://github.com/spantaleev/gitea-docker-ansible-deploy
- https://github.com/spantaleev/nextcloud-docker-ansible-deploy

In the near future, we'll be removing a lot of the shared role code from here
and using upstream roles for it. Some of the core `matrix-*` roles have
already been extracted out into other reusable roles:

- https://github.com/devture/com.devture.ansible.role.postgres
- https://github.com/devture/com.devture.ansible.role.systemd_docker_base
- https://github.com/devture/com.devture.ansible.role.timesync
- https://github.com/devture/com.devture.ansible.role.vars_preserver
- https://github.com/devture/com.devture.ansible.role.playbook_runtime_messages
- https://github.com/devture/com.devture.ansible.role.playbook_help

We just need to migrate to those.