Tutorials: Improve layout on Time Series tutorials

[amotl]

What's Inside

For adding dividers better conveying "What's Inside" each subsection of the "Data Analysis" section, i.e. which feature is demonstrated, use Sphinx' "rubric" directive.

Preview

• https://crate-cloud--65.org.readthedocs.build/en/65/tutorials/time-series.html#analyzing-data
• https://crate-cloud--65.org.readthedocs.build/en/65/tutorials/time-series-advanced.html#time-series-analysis-with-metadata