Table join docs need to be updated

[glookka]

Bug Description:

Table join docs need to be updated to include examples of explicit json field type conversion in ON condition.

Manticore Search Version:

6.3.1

Operating System Version:

Any

Have you tried the latest development version?

Yes

Internal Checklist:

^{To be completed by the assignee. Check off tasks that have been completed or are not applicable.}

• [ ] Implementation completed
• [ ] Tests developed
• [ ] Documentation updated
• [ ] Documentation reviewed
• [ ] Changelog updated