[skip ci] Version 2 RTD configuration file

As per email from RTD: The Read the Docs build system will start requiring a configuration file v2 (.readthedocs.yaml) starting on September 25, 2023.

Notes:

• This pull-request has no impact on v2 vs. v1 logical equivalence of the RTL, so the CI is skipped.
• This PR is the same as #825, this time for the dev branch (which is the branch currently used by RTD to render the User Manual).