Supersedes https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/2961

Related to e87f5c11d7

It seems like with the default versioning detection strategy (`docker`),
the version is detected up to the hyphen:

> Renovate tries to follow the most common conventions that are used to tag Docker images.
> In particular, Renovate treats the text after the first hyphen as a type of platform/compatibility indicator.

Perhaps with `semver` would be more appropriate for this image.

More details in: https://docs.renovatebot.com/modules/versioning/

Self-build now requires the new docker buildx/buildkit, so switch
from the ansible docker module to running a docker build command,
like elsewhere.

Without explicitly passing the `media_url` configuration,
Heisenbridge would try to guess it. It works most of the time,
but some people are experiencing trouble with it.

There's no need for wasteful work and for potential unreliability,
so we now configure the `media_url` explicitly.

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/2932

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