Specify attributes are case sensitive

[CaroFG]

It could be worth warning users that attributes are case sensitive, especially in the following guides:

• Configuring index settings with the Meilisearch Cloud interface
• Configuring index settings with the Meilisearch API

A free-trial customer was getting 0 search results, because he had copied the searchable attributes from the mini-dashboard, so all uppercase, so maybe worth mentioning something in the search preview page too?

[guimachiavelli]

IMO, it like we need to do two things about this:

1. fix the docs so that's stated explicitly
2. fix the search preview dashboard so attributes are displayed with correct capitalization

You could argue #2 is not super necessary, but it still seems like an easy enough thing to do and might serve as a subtle way of signalling capitalization is important.

[CaroFG]

I opened an issue in the mini-dashboard repo