[Task] Implement experimental gRPC binding

[eike-hass]

Description

Implement an experimental gRPC service to consume selected functions from the library.

Motivation

Allow arbitrary host languages to consume the library through a gRPC interface.

Resources

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To-do list

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• [ ] ...

Change checklist

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• [ ] 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.

### Tasks
- [ ] https://github.com/iotaledger/identity.rs/issues/1323
- [ ] https://github.com/iotaledger/identity.rs/issues/1328
- [ ] https://github.com/iotaledger/identity.rs/issues/1329
- [ ] https://github.com/iotaledger/identity.rs/issues/1330
- [ ] https://github.com/iotaledger/identity.rs/issues/1331
- [ ] https://github.com/iotaledger/identity.rs/issues/1335