* appservice: add and use matrix_homeserver_* vars

* appservice: use the new vars

* Apply suggestions from code review

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

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

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.

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

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/1939

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

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

`|to_json` already adds the surrounding double-quotes for the string, so
adding them explicitly means we've got a double-quotes problem.

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.

Discussed here: https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/1510

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.

We recently had someone need to inject additional configuration into
`/.well-known/matrix/client` as described here:
22b245bbd1/docs/bigbluebutton.md (have-dimension-create-meetings-with-elements-video-call-button)

There may be other use cases as well.

Seems like Ubuntu 18.04 does not have a dedicated `systemd-timesyncd` package, nor
does it include the `systemd-timesyncd` binary in the main `systemd` package.

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/1302

Regression since https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/1192

#1192 lead to the following error for me on Archlinux:
`TASK [matrix-base : Install host dependencies] *******************************************************************************************************************************
fatal: [matrix.***.de]: FAILED! => changed=false 
  msg: |-
    failed to install systemd-timesyncd: error: target not found: systemd-timesyncd`

There is no package called `systemd-timesyncd` on Archlinux. The service is installed with the [`systemd`](https://archlinux.org/packages/core/x86_64/systemd/) package itself.

I suggest removing the `systemd-timesyncd` from 2453876eb9/roles/matrix-base/tasks/server_base/setup_archlinux.yml (L7)