Add ability to block publishing per-checklist item

[mikeselander]

From our documentation, it appears that we can turn on blocking of publishing a post for all checklist items or not at all via altis.publication-checklist.block_on_failing config option.

However, it would be quite useful to make some checklist items blocking, but not all.

As an example, let's say we have two items on a publication checkilst:

1. Require a featured image.
2. Embargo date, whereby a post should never be published before it is over.

Item one is an important reminder, but should not block publishing a post in some situations. Item two is an absolute 100% must-never-happen item and this should always block an editor from publishing.

[huubl]

This would be very useful!

[roborourke]

This should be possible now that wp.data.dispatch('core/editor').lockPostSaving() accepts a string, so you can have multiple separate locks on publishing eg.:

wp.data.dispatch('core/editor').lockPostSaving('publication-checklist.featured-image')

// unlocking
wp.data.dispatch('core/editor').unlockPostSaving('publication-checklist.featured-image')