docs: update theme 1.8

[dgarcia360]

Related issue scylladb/sphinx-scylladb-theme#1229

ScyllaDB Sphinx Theme 1.8 is out 🥳!

Here's a summary of changes:

• Dark theme support for a fresh new look.
• Updated branding assets including new logos and mascots.
• Improved build process by recommending the inclusion of the poetry.lock file to ensure consistent dependencies in your CI/CD pipeline.
• New tooltip component to add more context to glossary terms, configuration parameters, or any other elements without cluttering the page.

You can read more about all the notable changes here.

How to test this PR

1. Clone this PR.

2. Enter the docs folder, and run:

   make preview
   

3. Open http://localhost:5500 in your browser. The doc should render without errors, and the version should be Sphinx Theme version (see the footer) must be 1.8.x:

   

[annastuchlik]

@zseta @zseta Could you review and merge this PR? This new theme version adds the dark theme, so it would be good to have it added across all ScyllaDB projects.

[annastuchlik]

@zseta ping