Fix api container tab update

[stonebuzz]

Checklist before requesting a review

Please delete options that are not relevant.

• I have performed a self-review of my code.
• I have added tests (when available) that prove my fix is effective or that my feature works.
• I have updated the CHANGELOG with a short functional description of the fix or new feature.
• This change requires a documentation update.

Description

• It fixes API update does not work with multiple blocks #835

From API, plugin need to check from $item->input to get related container instead of check $_REQUEST whioch is not relevant from API process

Screenshots (if appropriate):

[stonebuzz]

Ok from customer