Remove `AssignmentProviderConfig` and use parameters from `HostConfiguration` instead (#3181)
This PR removes `AssignmentProviderConfig` and uses the corresponding ondemand parameters from `HostConfiguration` instead. Additionally `scheduling_lookahead` and all coretime/ondemand related parameters are extracted in a separate struct - `SchedulerParams`. The most relevant commit from the PR is [this one](https://github.com/paritytech/polkadot-sdk/pull/3181/commits/830bc0f5). Fixes https://github.com/paritytech/polkadot-sdk/issues/2268 --------- Co-authored-by: command-bot <>