Allow for configurable service aggregators

Current situation

Some services differ only by the handlers they offer. One such example are providers: they are identical up to their handlers.

This leads to a possible inefficient use of resource (memory, mostly).

Desired outcome

A way to configure aggregated services, providers only for now.

This means a new aggregated section is available in the launcher manifest:

eventbus: python3 -m opentf.core.eventbus
services:
- ${{ CORE }}/core
plugins:
- ${{ CORE }}/plugins
- /app/plugins
aggregated:
- cucumber
- cypress
- robotframework
- junit
- postman
- skf
- soapui
disabled:
- dummyee
- localpublisher

Services in the aggregated list are not individually started, but are expected to be started by an aggregator service.

If you want to disable an aggregated service, you need to put it in the disabled section, as usual.

If a provider service is neither in the aggregated section nor in the disabled section, it will be started as usual, independently.