Create omni transaction docs

[thisisjoshford]

What?

Create documentation about omni-transaction-rs library. This is a library to allow one to create transactions for bitcoin, ethereum, and near inside of a near contract. Enables smart contract logic to happen on near ontop of these chains.

Why?

This is vital to the chain signatures ecosystem and there are no pages on this in the docs yet. It is also a pretty well put together library so documentation is ready to be added.

How?

• Create a couple examples using these library (near, ethereum + probably bitcoin).
• Write documentation for key parts of the examples (creating transaction, cross contract call to MPC, signature reconstruction, testing with mock MPC contract)
• Make sure all key concepts in this library are covered.

Resources

• Library https://github.com/near/omni-transaction-rs
• Examples, these are inside of a near contract but don't show fully how one would use these library, good to link to as a cookbook like we do in near-api-js https://github.com/Omni-rs/examples
• Full NEAR example (WIP) https://github.com/PiVortex/subscription-example
• We also have this abstract DAO example that creates an ethereum transaction inside of the contract but it does not use omni-transaction-rs, I would suggest that this example is moved over to using this library and this can fit in the same section of docs https://github.com/nearuaguild/abstract-dao/tree/main