Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/2090

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.

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/2076

* run the playbook on multiple hosts with different credentials with this script

* fix: add yaml missing document start "---"

* fix: *now really* allow this script to be run from any directory

* add about-note to examples/host.yml

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

* improve ansible-all-hosts.sh related docs/configuring-playbook.md

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

* fix typos :)

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

Doing this further simplifies examples/vars.yml.

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.

- caddy v1 requires a path in the header directive
- msisd has been replaced in favour of ma1sd

Seems to have been added by mistake.

Mostly affects people who disable the integrated `matrix-nginx-proxy`.

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/456
and more specifically 4d62a75f6f.

In short, this makes Synapse a 2nd class citizen,
preparing for a future where it's just one-of-many homeserver software
options.

We also no longer have a default Postgres superuser password,
which improves security.

The changelog explains more as to why this was done
and how to proceed from here.

Prompted by this: https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/779#issuecomment-764807507

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/570

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/641

Fixes #685 (Github Issue).

Fixes #586 (Github Issue)