[docs]: migrate lead/lag window function docs to new docs

[buraksenn]

Which issue does this PR close?

Partially #12936

Rationale for this change

Part of #12740

What changes are included in this PR?

• migrate to new doc
• delete lead/lag from static docs

Are these changes tested?

• documentation change

Are there any user-facing changes?

only documentation change

[Omega359]

Thank you for migrating this documentation! Would it be possible to add sql examples for each? If not I can file a followup PR to have those added to the docs for these functions and others that may be missing the examples.

[buraksenn]

Thank you for migrating this documentation! Would it be possible to add sql examples for each? If not I can file a followup PR to have those added to the docs for these functions and others that may be missing the examples.

I can add for lead/lag now in this PR. When I migrate window functions I can include sql examples

[alamb]

Thanks @buraksenn and @Omega359

Let's merge this PR in now and do the examples as a follow on. I would really like to get to the point where we have all the documentation migrated directly to the new pages.

🚀