[Task] Add support for DLT-less methods

## Description
Add support for additional DID methods that follow other CRUD implementations then `did:iota`. Off-chain methods like `did:key` or `did:jwk` can be a good proof of concept and are useful by themselfes.

## Motivation
Describe the motivation for the feature to be developed.

## Resources
Link to any resources relevant for the task such as issues, PRs, reference implementations, or specifications.

## To-do list

- [ ] refactor `did:key`
- [ ] add `did:jwk`
- [ ] add 'did:web'

## 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.

Start by comparing the existing CRUD implementations with did:iota, then investigate the requested did:key refactor and the proposed did:jwk and did:web methods. Define the implementation scope, bindings, tests, and documentation needed for each method; done means the supported methods build and have sufficient test coverage.

Written by the indexing model from the issue text.