ISBAT add an accordion item using a placeholder when interacting with the parent block

[richtabor]

Is this enhancement related to a problem? Please describe. After baking in a new UX pattern with omnipresent placeholders in the Menu/Menu Item block, we should consider adding this pattern to the Accordion block.

Describe the solution you'd like The Accordion block's "Add Accordion Item" appender should be replaced with a UX mechanism similar to the new Menu/Menu Item blocks, where a placeholder Accordion Item block appears when interacting with the block.

Current:

Proposed: