[Feature] deal_provider_collateral_bounds.

[ruseinov]

Summary of changes Changes introduced in this pull request:

• adds deal_provider_collateral_bounds and this_epoch_baseline_power to reward state in order to support the state_deal_provider_collateral_bounds RPC endpoint.

Reference issue to close (if applicable)

Closes

Other information and links

needs to be tested on forest first, once finalized could be reviewed and merged.

[ruseinov]

Now that I have realized that the actor code is actually copied from https://github.com/filecoin-project/builtin-actors, I'd say that we need to:

1. Introduce a shared helper for actor versions that don't define the deal_provider_collateral_bounds method (v8-v10).
2. Use the OG methods for other versions
3. Upgrade README.md with the reasoning as to why we can't actually introduce helpers for future versions (because that code is copied from the OG repo).

[ruseinov]

@LesnyRumcajs ready for re-review. feel free to merge when done