`matrix-postgres-backup` reuses the `matrix-postgres` role for these
tasks, not its own definitions.

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/2200

At some point, we can drop v9.6 support and use a single variable
that holds this value.

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/2191

fixes jitsi issue

ref: 57bb340343

We're starting it with `--user` and dropped capabilities, after all.

Hopefully fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/2188

We haven't encountered such a problem yet, but it doesn't hurt to
make things more robust.

These values that we were setting also make sense in the context of the
`matrix-postgres` role even when not used within the playbook.

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/2180

Just specifying `15` means we won't automatically re-pull `15.1` when it comes out.

We're overriding these in the correct way in `group_vars/matrix_servers`
so this wasn't causing any problem in practice.

.. when `matrix_nginx_proxy_enabled: false`

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/2177

These Postgres configuration variables are part of the `database.yaml` file
and don't need to be here.

This allows people to augment the Synapse image with custom tools and
addons without having to rebuild it from scratch.

If customizations are enabled, the playbook will build a new
`localhost/matrixdotorg/synapse:VERSION-customized` image
on top of the default one (`FROM matrixdotorg/synapse:VERSION`)
and with custom Dockerfile build steps.

For servers that self-build the Synapse image, the Synapse image will be
built first, before proceding to extend it the same way.

In the future, we'll also have easy to enable Dockerfile build steps
for modules that the playbook supports.

In the future, we'll also inject media storage providers that we support
into the `matrix_synapse_media_storage_providers_auto` list.

* fix room account data retrieving

* show recipient's email (header `TO`)
* add `norecipient` option
* add anti-spam options (`spamcheck:` and `spamlist:`)
* fix bugs