Update docusaurus

What does this MR do?

Updates docusaurus to the latest version: https://github.com/facebook/docusaurus/blob/master/CHANGELOG.md#200-alpha75-2021-04-30

Is there something that needs to be double checked?

Documentation is still working

Can this MR be accepted?

• I've read contribution guide
• Implemented
• Added/Updated tests
• Added/Updated documentation
• Pipelines passing

• Delete branch option set
• Fast-forwaded git merge is possible
• Added entry to CHANGELOG.md

Related issues

Closes #