This prevented us from keeping our workers reverse-proxying definitions
updated since Synapse v1.54.0.

The last `workers.md` file we could parse is at commit
02632b3504.
Parsing regressed at commit c56bfb08bc071368db23f3b1c593724eb4f205f0,
because the introduction message for `synapse.app.generic_worker` said
"If":

> If a worker is set up to handle a..

.. which made the AWK script think that definitions below were
conditional (which they're not in this case).

This patch fixes up the regex for determining if a line is conditional
or not, so that it doesn't trip up. Hopefully, it doesn't miss something
important.

1f196f59cb

This switches the `docker exec` method of spawning
Synapse workers inside the `matrix-synapse` container with
dedicated containers for each worker.

We also have dedicated systemd services for each worker,
so this are now:
- more consistent with everything else (we don't use systemd
instantiated services anywhere)
- we don't need the "parse systemd instance name into worker name +
port" part
- we don't need to keep track of PIDs manually
- we don't need jq (less depenendencies)
- workers dying would be restarted by systemd correctly, like any other
service
- `docker ps` shows each worker separately and we can observe resource
usage

(allegedly breaks with SSO enabled)

(yes, a bit awkward and brittle… xD)

also, worker.yaml.j2:
  - hone worker_name
  - remove worker_pid_file entry (would only be used if worker_daemonize
    set to true; also, synapse only knows about the container namespace
    and thus can not provide the required host-view PID)