Time to update theme for RTD docs GenPipes

[shaloo]

During the E2E review #301 the following was discovered, needs discussion and action accordingly.

We are using a very old RTD theme discuss with the team and suggest more modern doc themes such as https://pydata-sphinx-theme.readthedocs.io/en/stable/ that already have banner and other components pre-built and customizable for docs. Also see, https://sphinx-design.readthedocs.io/en/furo-theme/ as another option that is used by several docs hosted at RTD.