Issues and Pull Requests were not migrated to the new
organization/repository, so `matrix-org/synapse/pull` and
`matrix-org/synapse/issues` references were kept as-is.

`matrix-org/synapse-s3-storage-provider` references were also kept,
as that module still continues living under the `matrix-org` organization.

This patch mainly aims to change documentation-related things, not actual
usage in full yet. For polish that, another more comprehensive patch is coming later.

Completely untested.

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/1544

This may be especially helpful to existing playbook users
who happen to find themselves installing Go-NEB later on.