[Feature] Add Kapa.ai docs assistant integration to DolphinScheduler

Search before asking

• I had searched in the issues and found no similar issues.

What happened

We already applied for and got access to Kapa.ai for the DolphinScheduler project. I’d like to propose that we integrate the Kapa.ai documentation assistant into our docs of https://github.com/apache/dolphinscheduler-website

Previously, DolphinScheduler had a corresponding PR. However, at that time, the act of connecting to the AI Q&A was not approved by ASF, so the PR was rolled back. You can refer to that PR.

Why

• DolphinScheduler has a lot of concepts and configuration options.
• New users often ask repeated “how to configure X / why does Y fail” questions.
• A docs-grounded AI assistant can help users find answers faster and reduce basic Q&A.

What needs to be done

Docs site integration

• Embed the Kapa “Ask AI” widget <script> snippet into the official documentation site layout, so users can ask questions on any docs page.

Are you willing to submit PR?

• Yes I am willing to submit a PR!

Code of Conduct

• I agree to follow this project's Code of Conduct