Add a list of (changed) rendered files to the "docs emitted" PR comment

[AetherUnbound]

Description

Presently we have a step in our CI/CD which builds the docs in a preview directory, then emits a message saying as much with a path to the main preview page:

openverse/.github/workflows/ci_cd.yml

Line 769 in 399036e

emit-docs:

Recently, @obulat added an edited note on the comment to help community contributors view the rendered project plan easier: #2637 (comment)

It would be ideal if we could generate a list of the doc files which have been changed or differ from main, and then display that inside the comment as well. This might be possible using simple directory diffing at this step:

openverse/.github/workflows/ci_cd.yml

Lines 824 to 829 in 399036e

	- name: Replace preview of current PR
	if: github.event_name == 'pull_request'
	run: |
	cp -r . /tmp/gh-pages
	sudo rm -rf /tmp/gh-pages/_preview/${{ github.event.pull_request.number }}
	mv /tmp/docs /tmp/gh-pages/_preview/${{ github.event.pull_request.number }}

We'd need to account for scenarios which potentially change all (dozens at this point?) of the files in the docs directory. Perhaps we after a certain limit we can emit a message that says "too many files changed to reference each individually".