[Feature][Doc] Add doc about connector-v2 schema feature

[Hisoka-X]

Search before asking

• [X] I had searched in the feature and found no similar feature requirement.

Description

SeaTunnel support schema config in connector-v2. But we don't have any document to introduce this feature. We should:

1. Add new document about schema feature. Introduce why we need schema? What type we supported at now? How to use schema? When we should use it or not?
2. Add doc to docs/en/concept.
3. Link it into website use sidebars.js
4. (Option) Modify connector doc to link to this doc which use schema.

Usage Scenario

No response

Related issues

No response

Are you willing to submit a PR?

• [ ] Yes I am willing to submit a PR!

Code of Conduct

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

[Hisoka-X]

@liugddx PTAL