Update 1.8 release docs

[dgarcia360]

Updates the 1.8 release docs with the latest additions.

Message for announcement

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.

For a migration guide, check out Upgrading from 1.7 to 1.8.

[annastuchlik]

LGTM