Add indicator for modified post meta in pre-publish flow

[artemiomorales]

What problem does this address?

Follow up to https://github.com/WordPress/gutenberg/pull/61811

While we are now indicating to users when metadata has changed to published posts, we do not yet do so when a post is still in pre-published state.

We should determine what this UX should be and any revisions that would be needed to accommodate this in the pre-publish flow.

What is your proposed solution?

One idea: We can consider integrating information about the post meta in the pre-publish check as another collapsed panel next to suggestions related to tags and categories, as observed in this comment.

We should also consider surfacing this information whenever a draft is saved.

[artemiomorales]

If we were to show the meta changes in the pre-publish flow as a panel, what would we put in it? This is what two of the other panels look like expanded:

We could just include the modified meta shown in the following Posts panel from https://github.com/WordPress/gutenberg/pull/62982:

I don't believe the "Posts" heading would work in this case. Perhaps it should say "Meta"? Other aspects of the panel would also need to change, including:

• Removing "There is X site change(s) waiting to be saved"
• Removing "Post Meta"
• Removing the post name, since we'll be in the post editor and displaying the name would be redundant

Maybe it could look something like this:

[jasmussen]

@jarekmorawski I feel like you had some good instincts in past conversations around bindings and such. Since some of the work I've provided here has not sailed through smoothly, I wonder if you would have time at some point in the 6.7 phase to revisit something like this issue with a fresh perspective? Past Figma work.

[SantosGuillamot]

I've opened this new issue trying to gather all the context related to the save workflows and post-meta/post-data. I think it is important to take one step back and think about it more broadly.