As reported in https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/3451#issuecomment-2331316593

Likely the solution to https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/3451

No need to duplicate the same logic as in `group_vars/matrix_servers`.

Having it disabled by default in the role itself and overriding it at the playbook level (based on the selected homeserver implementation) makes more sense.

This is provoked by de91fe933d94afcdbfdb0c6cf75a1dfa43dfdf43,
where I've added a few new labels and made it possible for people to
disable them.

In this patch, I'm making it possible to disable any of the old Traefik
labels in a similar way.

Related to:

- https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/3409
- https://github.com/t2bot/matrix-media-repo/releases/tag/v1.3.5
- https://github.com/matrix-org/matrix-spec-proposals/pull/3916

Support for authenticated media routes is enabled by default, but
variables are in place to disable it if necessary.

This change has not been tested.

`matrix-media-repo` is the only role that seems incompatible with the
changes introduced by Traefik v3, due to its use of `PathPrefix` with
regular expressions in a few places.

Regular expressions should now be used with `PathRegexp`, not
`PathPrefix`. Furthermore, they should follow the Golang regexp syntax,
as described in the migration guide:
https://doc.traefik.io/traefik/migration/v2-to-v3-details/#dynamic-configuration-changes

Fixup for f97e849018

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/3354

Continuation of 9f2eff2ac7

Provoked by 7749048bf8
(https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/3353)

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/3349

`docker.io/turt2live/matrix-media-repo:v1.3.4` is amd64-only.

`ghcr.io/t2bot/matrix-media-repo:v1.3.4` is a multi-arch image which
works on arm64.

This is mostly so as to avoid referring to variables from other roles,
like `matrix_nginx_proxy_proxy_matrix_client_api_addr_with_container`.

This should come (and already does) from group_vars/matrix_servers

`matrix_media_repo_identifier` is already defined in the role defaults,
which is a better role to have it anyway.

* Updated MMR docs with updated fields in main.yaml

* Removed uneeded placeholder db password

This is backward-compatible with what we had before. We're not changing
the SSL mode - just making it configurable.

Most components are defaulting to `sslmode=disable`, while some
(`matrix-bot-matrix-reminder-bot` and others) do not specify an `sslmode` at all.

We're making sslmode configurable, because certain external Postgres
servers may be configured to require SSL encryption.
In such cases `sslmode=disable` does not work and needs to be changed to
`sslmode=require` or something else (`verify-ca`, `verify-full`, etc).