Move configuration (at least the per-participant config) to the "reports" repository

[yrodiere]

The Quarkus repo is (rightly) a bit strict about what we allow to merge, and in particular requires approval before merging.

That's annoying when someone just wants to change something to their participant config, such as the max number of issues for a given category.

We should consider moving part of the configuration to the "reports" repository. Either:

1. put the all config in quarkusio/quarkus-github-lottery
2. put the main config in quarkusio/quarkus and per-participant config in quarkusio/quarkus-github-lottery
3. put the main config in quarkusio/quarkus and per-participant config in the main description of per-participant issues quarkusio/quarkus-github-lottery

We could also add a command such as /lottery subscribe to have configuration initialized. That would be necessary for item number 3 in particular, since initializing a per-participant issue is not trivial.