Patch contributed by JulianF.

Seems like we don't necessarily need to use a public URL for `SYNCV3_SERVER`.

This possibly helps setups that were having trouble when `SYNCV3_SERVER`
was a public URL (e.g. `https://matrix.DOMAIN`), as described in:
https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/2912

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/2923

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/2919

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/2918

Related to https://github.com/matrix-org/synapse/pull/15488

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/2905#issuecomment-1726892215

Many of these do depend on the Synapse master process (`matrix-synapse.service`),
so it makes sense to do it.

Furthermore, we're doing it so that one can stop the `matrix-synapse.service`
service and have systemd cascade this into stopping all the workers as well.

This is useful for easily stopping all of Synapse, so that Postgres
upgrades (`--tags=upgrade-postgres`) can happen cleanly.
Postgres upgrades currently stop `devture_postgres_systemd_services_to_stop_for_maintenance_list` which
includes Synapse, but stopping just the master process and leaving workers running is not safe enough and sometimes leads to errors like:

> ERROR:  insert or update on table "event_forward_extremities" violates foreign key constraint "event_forward_extremities_event_id"

With this dependency in place, stopping `matrix-synapse.service` will stop all Synapse processes.

Related to https://github.com/matrix-org/synapse/pull/16265

Draupnir moved its repo on github from the namespace of its maintainer Gnuxie to a newly created Github Organisation the-draupnir-project and this commit reflects this.

Draupnir changed home from Gnuxie/Draupnir to the-draupnir-project/Draupnir and this commit reflects this.