Add sr25519 keys

[i1i1]

Description

This pr is followup of spec issue. It adds support for sr25519 keys for libp2p.

Links to any relevant issues

• https://github.com/libp2p/specs/issues/409

Open Questions

Change checklist

• [x] I have performed a self-review of my own code
• [x] I have made corresponding changes to the documentation
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] A changelog entry has been made in the appropriate crates