Mkdocs-section-index

* Compatibility with mkdocs-material 8.2.8+: https://github.com/oprypin/mkdocs-section-index/commit/f43f39741223735f53615a78a9383d924fcaf6c5, #10

* Fix templates to support mkdocs-material version 7.3: https://github.com/oprypin/mkdocs-section-index/commit/f4b1e5bf53b04eb057f68511754e754c0f5e4295, #7

* Fix MkDocs sitemap to not skip section index pages: 7ecc3083303dc9c7700ebbf403abe4480ada02b8
* Fixes Material theme's `navigation.instant`
* Skip rendering navs of non-active tabs: ca3af56a1beb388852ee0987bb13726fbfaa46fa
* Warn when a plugin later in the list replaces the nav: 145ce693fa86d950e602fc8f6eab1ea29c8be236

* Adapt to mkdocs-material version 6.2

* Material theme: support [navigation-tabs](https://squidfunk.github.io/mkdocs-material/setup/setting-up-navigation/#navigation-tabs)