Forms: Add the possibility to add a link to the checkbox's label

### What

When using the Form Block, the checkbox's text (=label) cannot include an embedded link.


A user requests to include the possibility for the text to include a link.

Context: 6212555-zd-woothemes

### Why

It makes sense for usability.

### How

_No response_

### Workaround

We can create this look: 

Add a Row block. Include the Checkbox and a Paragraph block. Adjust Checkbox layout settings to be `0 rem` and the Row block's padding to be `1rem`. Add a background color for even more visibility.

Start by locating the Jetpack Form Block implementation for the checkbox label and review any existing form-block tests. Confirm how label text is currently rendered, then define done as allowing an embedded link in that label while preserving the checkbox layout and verifying the resulting form behavior.

Written by the indexing model from the issue text.