[Task] Add credential and presentation examples

[PhilippGackstatter]

Description

Add examples for creating, signing, verifying and revoking credentials and presentations. These should match the examples from 0.6 in functionality as much as possible.

Motivation

Example parity with the 0.6 version.

Resources

• https://github.com/iotaledger/identity.rs/blob/support/v0.6/examples/account/create_vc.rs
• https://github.com/iotaledger/identity.rs/blob/support/v0.6/examples/account/create_vp.rs
• https://github.com/iotaledger/identity.rs/blob/support/v0.6/examples/account/revoke_vc.rs

To-do list

Create a task-specific to-do list. Please link PRs that match the TODO list item behind the item after it has been submitted.

• Port the examples listed in Resources for Rust and Wasm.

Change checklist

Add an x to the boxes that are relevant to your changes, and delete any items that are not.

• The feature or fix is implemented in Rust and across all bindings whereas possible.
• The feature or fix has sufficient testing coverage
• All tests and examples build and run locally as expected
• Every piece of code has been document according to the documentation guidelines.
• If conceptual documentation (mdbook) and examples highlighting the feature exist, they are properly updated.
• If the feature is not currently documented, a documentation task Issue has been opened to address this.

[abdulmth]

Wasm examples still missing