Introduce Compute Limit chunk property

[aborg-dev]

With the introduction of Compute Costs the chunk now also has a Compute Limit beside the usual Gas Limit. At the moment Compute Limit matches the Gas Limit.

This introduces some confusion in the code where we assign gas limit to compute limit. To resolve this, we need to answer the following questions:

• [ ] Gas limit is no longer used to limit the chunk capacity. What else is it used for? Can we fully replace it with compute limit?
• [ ] Do we expect any other limits to be introduced in the future? E.g. Disk IOPS limit or Network usage limit.