Clean up unnecessary overwrites (custom CSS, layouts, JS)

[ialidzhikov]

/kind cleanup

What would you like to be added:

• Clean up the unnecessary overwrites that we currently have:
  • custom CSS
  • docsy/hugo layouts
  • JS
• Check if _index.md gets created in docs
• Display better the alerts added with Add support for Github notes syntax #230.

What functionality should be preserved:

• clicking of links from API references should scroll to target
• look good on most resolutions
• ...

Why is this needed:

• Easier maintenance (The website won't break when we update the docsy/hugo version)
• Better outlook - the default docsy outlook

[ialidzhikov]

/assign @Kostov6 @RadaBDimitrova