feat: call in did creation

[weichweich]

Convenience for the DID creation

fixes https://github.com/KILTprotocol/ticket/issues/1897

Creating a DID and setting all keys requires two signatures. Submitting a call with the create op reduces this to one.

Checklist:

• [ ] I have verified that the code works
  • [ ] No panics! (checked arithmetic ops, no indexing array[3] use get(3), ...)
• [ ] I have verified that the code is easy to understand
  • [ ] If not, I have left a well-balanced amount of inline comments
• [ ] I have left the code in a better state
• [ ] I have documented the changes (where applicable)