We need this to control whether `('matrix-' + matrix_homeserver_implementation + '.service')`
would get injected into `devture_systemd_service_manager_services_list_auto`

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.

This mostly fixes `key-order` warnings around
`block` statements.

Reference: https://ansible-lint.readthedocs.io/en/latest/default_rules/#var-naming

We don't really fix these, but just suppress them,
because they're like that intentionally.

We try to name variables in a way that is consistent with the
configuration key they control. If the upstream component uses
camelCase, we also need to include camelCase in the variable name.

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/1931

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/1931

* Implement MSC 1929 Homeserver Admin Contact
Fixes #1612

For details to the proposed (not accepted yet) MSC, see:
https://github.com/matrix-org/matrix-spec-proposals/blob/hs/proposal-admin-contact-1/proposals/1929-admin-contact.md

* Implement feedback from PR #1931

* Implement feedback from PR #1931

* Fix mixed indentation

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.

Various roles depend on this. It makes sense to make it part
of the `matrix-base` role.

Fedora 35 is:

- `ansible_os_family = 'RedHat'`
- `ansible_distribution_major_version = '35'`

Our RedHat checks against v7/v8 are really for RHEL derivatives (CentOS, Rockylinux,
AlmaLinux), but the same checks (by coincidence) apply for Fedora 35.

The problem is that `'35' > '7'` (comparing these as strings) is
`false`.

This patch makes sure that we always cast
`ansible_distribution_major_version` to an integer.

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/1610

Not hardcoding 'CentOS' and using the OS family ('RedHat') instead,
we now behave better on Rockylinux and AlmaLinux, etc.

With that said, we may or may not fully support CentOS/Rockylinux/AlmaLinux v8 yet.
Certain things were improved in
https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/300.

v8 support is discussed here: https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/300
Certain things (firewalld?) may still be problematic. This patch does not try to address those.
If the remaining issues are confirmed to be fixed in the future, we can mark v8 as supported.

We're trying to move away from implementation-specific variables,
hoping for a clean (implementation-neutral) examples/vars.yml file.

Doing this seems more reasonable and simpler.

Also get rid of `--tags=update-user-password` in the
`matrix-dendrite` role, as what we had doesn't work.

We may be able to do it with some Ansible helper or something else.
For now, we'll omit this feature.

The goal is to have a single variable which tells us which homeserver
software is in use. Much simpler than having if/elif/elif checks for
variables like (`matrix_synapse_enabled` and `matrix_dendrite_enabled`, etc.)
everywhere.