[Task] Create verification method

## Description
Parameter: DID, Crypto Type, VerificationRelationship
Returns: Fragment, Storage keyid

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

- [ ] Item one
- [ ] Item two
- [ ] Item three

## 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 finding the existing Rust APIs for DID, crypto types, verification relationships, fragments, and storage key IDs. The issue provides no file, entry point, motivation, specification, or concrete TODO items, so clarify the intended behavior and required bindings before implementation. Done should include the verification method and sufficient tests, with builds and documentation updated as applicable.

Written by the indexing model from the issue text.