Support eth_getProof JSON RPC method

[fedejinich]

Support eth_getProof JSON RPC method

Description

Described at RSKIP251

Motivation and Context

This new method it's useful for offchain state verifications. Just by having a safe block header, a user can ask proofs and validate an account state or storage values.

Solves #1493

How Has This Been Tested?

• Unit tests
• DSL Tests (todo)

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• Tests for the changes have been added (for bug fixes / features)
• Requires Activation Code (Hard Fork)

• Other information:
• https://eips.ethereum.org/EIPS/eip-1186
• https://medium.com/coinmonks/spv-proofs-explained-f38f8bb8f580
• https://medium.com/shyft-network-media/understanding-trie-databases-in-ethereum-9f03d2c3325d
• https://blog.rsk.co/noticia/towards-higher-onchain-scalability-with-the-unitrie/

[fedejinich]

still need to add DSL test cases and resolve remainings todos (minnor stuff). The overall functionality can be reviewed