MBT: Add reward distribution

[p-offtermatt]

This is an issue that tracks the progress on adding reward distribution: https://cosmos.github.io/interchain-security/features/reward-distribution

Several main tasks should be done:

1. Adjust the Quint model to include the feature
2. Add tests in Quint to test the feature
3. Make sure that the generated traces use the feature in non-trivial ways (or add new generation methods, i.e. invariants, that do)
4. Expand the driver to understand/utilize the new feature