Support registering Application Services when running with workers under Complement.

[reivilibre]

This goes towards fixing #12825.

[clokep]

I can't find any documentation for absolute(). Kind of sounds like resolve()?

[reivilibre]

Huh, weird

>>> from pathlib import Path
>>> p = Path("/tmp")
>>> p.absolute()
PosixPath('/tmp')
>>> p.__class__
<class 'pathlib.PosixPath'>
>>> help(p.absolute)

Help on method absolute in module pathlib:

absolute() method of pathlib.PosixPath instance
    Return an absolute version of this path.  This function works
    even if the path doesn't point to anything.
    
    No normalization is done, i.e. all '.' and '..' will be kept along.
    Use resolve() to get the canonical path to a file.

Nothing against using resolve, this just seemed more intuitive to use (no idea why it's not documented!)

[clokep]

It is likely fine, was just confused. 🤷

[clokep]

This exists on the non-worker version:

synapse/docker/conf/homeserver.yaml

Lines 164 to 168 in 66a3f2f

	{% if SYNAPSE_APPSERVICES %}
	app_service_config_files:
	{% for appservice in SYNAPSE_APPSERVICES %} - "{{ appservice }}"
	{% endfor %}
	{% endif %}

[reivilibre]

This exists on the non-worker version:

synapse/docker/conf/homeserver.yaml

Lines 164 to 168 in 66a3f2f

	{% if SYNAPSE_APPSERVICES %}
	app_service_config_files:
	{% for appservice in SYNAPSE_APPSERVICES %} - "{{ appservice }}"
	{% endfor %}
	{% endif %}

That's not the Complement one.

The non-docker one I looked at does some.. sed nastiness..

synapse/docker/complement/conf/homeserver.yaml

Lines 108 to 109 in 4fef76c

	app_service_config_files:
	AS_REGISTRATION_FILES

synapse/docker/complement/conf/start.sh

Lines 8 to 18 in 4fef76c

	for filename in /complement/appservice/*.yaml; do
	[ -f "$filename" ] || break
	as_id=$(basename "$filename" .yaml)
	# Insert the path to the registration file and the AS_REGISTRATION_FILES marker after
	# so we can add the next application service in the next iteration of this for loop
	sed -i "s/AS_REGISTRATION_FILES/ - \/complement\/appservice\/${as_id}.yaml\nAS_REGISTRATION_FILES/g" /conf/homeserver.yaml
	done
	# Remove the AS_REGISTRATION_FILES entry
	sed -i "s/AS_REGISTRATION_FILES//g" /conf/homeserver.yaml

(sigh)

In the workers case, we have Jinja2 so I thought it would be nicer to use that instead.
Note we have to scan the directory for all the appservices, so I thought doing that in Python was a little less yucky than having a space-separated env variable or something like that.