feat: implement WebRTC certificate sotorage in the keychain

[Crosstons]

Title

feat: Implement WebRTC certificate persistence

Description

This PR implements the WebRTC certificate persistence functionality. The following changes have been made:

• Added certificate-store.ts to handle storing and retrieving certificates from the keychain.
• Created tests for certificate persistence in certificate-persistence.spec.ts.

This addresses the issue of ensuring certificates can be stored and reused across node restarts, improving the reliability and efficiency of WebRTC connections.

Related #2988.

Notes & open questions

• The test file certificate-persistence.spec.ts contains two tests. One test passes successfully, while the second test related to persisting certificates between restarts still needs changes. Further debugging and adjustments are required to ensure all tests pass.

Change checklist

• I have performed a self-review of my own code
• I have made corresponding changes to the documentation if necessary (this includes comments as well)
• I have added tests that prove my fix is effective or that my feature works