GHA workflow to build the debs

Signed-off-by: Dirk Klimpel <dirk@klimpel.org>

Signed-off-by: Dirk Klimpel <dirk@klimpel.org>

Fixes #10325

We might have events in the staging area if the service was restarted while there were unhandled events in the staging area.

Fixes #10295

Fix link in modules doc to point at instructions on registering a callback instead of ones on registering a web resource.

Instead of mixing them with user authentication methods.

this was a typo introduced in #10282. We don't want to end up doing the
`replace_stream_ordering_column` update after anything that comes up in
migration 60/03.

Now that we've fixed it.

Related to #10251

The presence router docs include some sample homeserver config. At some point we changed the name of the [config option](https://github.com/matrix-org/synapse/blob/859dc05b3692a3672c1a0db8deaaa9274b6aa6f5/docs/sample_config.yaml#L104-L113), but forgot to update the docs.

I've also added `presence.enabled: true` to the example, as that's the new way to enable presence (the `presence_enabled` option has been deprecated).

We need to rebuild *all* of the indexes that use the current `stream_ordering`
column.

This broke in #10272