feat: btc interfaces

[wainola]

I'm using @mpetrunic #359 as base to have folder structure

Description

Related Issue Or Context

Closes: #376

How Has This Been Tested? Testing details.

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 change)
• [ ] Documentation

Checklist:

• [ ] I have commented my code, particularly in hard-to-understand areas.
• [ ] I have ensured that all acceptance criteria (or expected behavior) from issue are met
• [ ] I have updated the documentation locally and in chainbridge-docs.
• [ ] 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