Improve docusaurus configuration

[julienrbrt]

Follow-up of #13471.
Smalls tasks were left to improve the website:

• create components for having a similar look that the https://docs.cosmos.network/v0.46/ page
• resolve +++ for displaying code snippet
  • We probably need to fork and fix https://github.com/saucelabs/docusaurus-theme-github-codeblock
  • Or port our own script https://github.com/cosmos/vuepress-theme-cosmos/blob/develop/markdown-it-gh.js
• find a way to clean-up algolia index (many 404 links from unsupported versions)

[rootulp]

find a way to clean-up agolia index (many 404 links from unsupported versions)

In addition to the 404 results, there are search results that don't display any content (see screenshot in #13544).