Refactor resource manager (#6322)

Refactor resource manager (#6322)

This PR does another round of refactoring of the resource manager and related code.

- it moves the Resource enum out of the ResourceManager class
- it treats the resources in a generic way (storing the statistics in a vector) instead of the manual treatment we had before
- weights no longer live in the options, but in the ResourceManager and are changed accordingly in the ResourceManager constructor
- following the generic treatment of resources, it also removes all the resource-specific options --x-step in favor of a generic --rweight name=weight
- removed several unused methods from the ResourceManager

Note that we handle the Resource enum in a way that allows to easily use other enums as additional resources, for example InferenceId. The general idea is that we will at some point have sensible default weights (so that the cumulative resources somewhat simulate the solver runtime) and users (almost) never need to modify them.