* 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>

Regression since 1693c4ca1d

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/1975

Reference: https://ansible-lint.readthedocs.io/en/latest/default_rules/#no-changed-when

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

Details here: https://docs.ansible.com/ansible/devel/porting_guides/porting_guide_6.html#id36

Basically:

```yaml
- name: Prior to 2.13
  debug:
    msg: '[1] + {{ [2] }}'

- name: 2.13 and forward
  debug:
    msg: '{{ [1] + [2] }}'
```

Interestingly, we had been using the new/safe syntax in lofs of places.

We were using the broken one in many others though. Hopefully all
instances were fixed by this patch.

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/1749

The `to_nice_yaml` helper will by default wrap any string YAML values on
the first space after column 80. This can in worst case yield invalid
YAML syntax. More details in Ansible's documentation here:

https://docs.ansible.com/ansible/latest/user_guide/playbooks_filters.html#formatting-data-yaml-and-json

In short, you need to explicitly provide a custom width argument of a
high number of some kind to avoid the line wrapping.

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/1480

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/1242

Until now, we were leaving services "enabled"
(symlinks in /etc/systemd/system/multi-user.target.wants/).

We clean these up now. Broken symlinks may still exist in older
installations that enabled/disabled services. We're not taking care
to fix these up. It's just a cosmetic defect anyway.

This bridge doesn't support SQLite anyway, so it's not necessary
to carry around configuration fields and code for migration from SQLite
to Postgres. There's nothing to migrate.