Closes #477

Adds instructions to trigger pull requests previews only when there are updates within the docs/ folder.

How it works

The workflow provisions an instance and checks if there are differences between the docs folder of the pull-request and the one in the master branch. If not, skips the build and publication steps.

Limitations

• The workflow still runs to provision the instance and make the diff, but takes 1:40 minutes instead of 4:30 minutes in the scylla/scylla-docs project.

• AWS Amplify posts a message on the GitHub issue, even if the build & deploy process is not triggered:

Unfortunately, the tool does not offer an option to disable this message. However, we can open an issue on the amplify repo, hoping AWS adds this option in the future or try to delete the message with a custom GitHub Action: #540

Next steps

• @dgarcia360 Send a PR to the scylladb/carepet to add the new amplify.yml file.
• @tzach Follow the new instructions to build only docs if the docs folder is updated.
• @dgarcia360 (Optional) Look for a custom docker image that has Python 3.8 installed by default to slightly reduce the build time of previews. [Amplify] Optimize previews build time #533