Stardust DID Method Proof-of-Concept

[cycraig]

Description of change

Add the identity_stardust sub-project to isolate the development environment of the UTXO-based DID Method for the time being. Currently this is just a skeleton to build atop: it is not integrated into the Wasm bindings yet.

There are separate GitHub CI steps and jobs (@eike-hass please review) since identity_stardust is not part of the root workspace (due to compilation issues), and thus has a separate target directory and cache. Only tested on ubuntu-latest for now.

Includes a short example on creating a DID Document and embedding it in an AliasOutput, then resolving it via the Indexer API exposed by iota-client.

cd identity_stardust && cargo run --example create_did

Links to any relevant issues

See #908.

Type of change

• 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

Manually tested with example. New GitHub CI jobs added for identity_stardust.

Change checklist

• 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