Add search link type in the extractor

[Sola0404]

• [x] I carefully read the contribution guidelines and agree to them.
• [x] I have tested the API against NewPipe.
• [x] I agree to create a pull request for NewPipe as soon as possible to make it compatible with the changed API.

[FireMasterK]

Looks almost good to me. @FireMasterK could you take a look, too? Also, do we need tests for the link handler?

Honestly, I don't know how this part of the extractor works at all, so I would be the wrong candidate.

We likely do need tests, since I did check the Channel link handler, which has tests.

[Stypox]

@Sola0404 do you plan to keep working on this? Also, you should also implement this for all other services, and not just for youtube, if possible (shouldn't be too difficult though).