Fix Transaction handling for WASM on testnet

[wulfraem]

Description of change

Fixes issues with Fix Transaction handling for WASM on testnet:

• testnet faucet only returns one coin, so coin lookup had to be updated, now works basically the same as the lookup in Rust.
• A gas budget can now be set when creating identities and/or when updating DID documents. Similar to proposal, gas budget can be set with with_gas_budget function or with gasBudget setter on transaction.
• Default gas budget in WASM transaction has been lowered to usual value of 50_000_000.

Type of change

Add an x to the boxes that are relevant to your changes.

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

How the change has been tested

Tested local to local, and from local to testnet. For overall validation, waiting for CI.

Change checklist

Add an x to the boxes that are relevant to your changes.

• I have followed the contribution guidelines for this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes