Add RLP Header to Sig Verif struct + merge changes from main

[waymobetta]

Description

• Added RLP Header field (type []byte) to the Signature Verification struct.

This encodes the entire block header which will then be used within the proof verification process

• Added utility function to generate data to be stored within this RLPHeader field
• Added test of this utility function
• Added generateBlockHeader for testing
• Modified existing tests to pass with additional field in Signature Verification struct (even though this code is ignored)

Note: I could probably have gotten away with not creating a new function for this but it seemed like a good idea for testing purposes.

Related Issue Or Context

Closes: #118

How Has This Been Tested? Testing details.

Made test as well as modified existing

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)
• [ ] Documentation

Checklist:

• [x] I have commented my code, particularly in hard-to-understand areas.
• [x] I have ensured that all acceptance criteria (or expected behavior) from issue are met
• [ ] I have updated the documentation locally and in chainbridge-docs.
• [x] I have added tests to cover my changes.
• [ ] I have ensured that all the checks are passing and green, I've signed the CLA bot

[github-actions[bot]]

Go Test coverage is 40.9 %\ :sparkles: :sparkles: :sparkles:

[github-actions[bot]]

Go Test coverage is 40.9 %\ :sparkles: :sparkles: :sparkles:

[P1sar]

why draft?