docs: update theme 1.2

[dgarcia360]

Related issue https://github.com/scylladb/sphinx-scylladb-theme/issues/395

ScyllaDB Sphinx Theme 1.2 is now released 🥳

We’ve added automatic checks for broken links and introduced numerous UI updates.

You can read more about all notable changes here.

How to test this PR

1. Clone this PR. For more information, see Cloning pull requests locally.

2. Enter the docs folder, and run:

make preview

4. Open http://127.0.0.1:5500/ with your favorite browser. The doc should render without errors, and the version should be Sphinx Theme version (see the footer) must be 1.2.x:

[dgarcia360]

The new link checker complains about the following broken links:

[quick-start\grafana\provisioning\plugins\grafana-piechart-panel\README.md]:
✗ [504] https://david-dm.org/grafana/piechart-panel | Network error: Gateway Timeout
✗ [504] https://david-dm.org/grafana/piechart-panel/dev-status.svg | Network error: Gateway Timeout
✗ [504] https://david-dm.org/grafana/piechart-panel.svg | Network error: Gateway Timeout
✗ [504] https://david-dm.org/grafana/piechart-panel/?type=dev | Network error: Gateway Timeout
✗ [403] http://docs.grafana.org/v3.0/plugins/installation/ | Network error: Forbidden

[rust\README.md]:
✗ [ERROR] file:///C:/Users/dgarc/scylladb/care-pet/rust/scylla-rust-driver | Cannot find file

[java\README.md]:
✗ [404] http://maven.apache.org/POM/4.0.0 | Network error: Not Found
✗ [ERROR] file:///C:/Users/dgarc/scylladb/care-pet/java/docs | Cannot find file

[quick-start\grafana\provisioning\plugins\camptocamp-prometheus-alertmanager-datasource\README.md]:
✗ [404] https://raw.githubusercontent.com/camptocamp/grafana-prometheus-alertmanager-datasource/master/images/overview.png | 
Network error: Not Found
✗ [404] https://raw.githubusercontent.com/camptocamp/grafana-prometheus-alertmanager-datasource/master/images/table.png | Network error: Not Found

[quick-start\grafana\provisioning\plugins\camptocamp-prometheus-alertmanager-datasource\dist\README.md]:
✗ [404] https://raw.githubusercontent.com/camptocamp/grafana-prometheus-alertmanager-datasource/master/images/table.png | Network error: Not Found
✗ [404] https://raw.githubusercontent.com/camptocamp/grafana-prometheus-alertmanager-datasource/master/images/overview.png | 
Network error: Not Found

[docs\build-with-go.md]:
✗ [ERROR] file:///C:/getting_started.md | Cannot find file

[quick-start\grafana\provisioning\plugins\scylla-plugin\README.md]:
✗ [404] https://circleci.com/gh/grafana/simple-datasource-backend/tree/master | Network error: Not Found
✗ [404] https://circleci.com/gh/grafana/simple-datasource-backend/tree/master.svg?style=svg | Network error: Not Found       

Could you please fix them in a separate pull request? Thanks!