Add IgnoreCase to repository queries documentation.

Update reference documentaion and add missing IgnoreCase keyword.

Closes: #3916
Original Pull Request: #3950

Author: mihailcornescu

src/main/asciidoc/reference/mongo-repositories.adoc

@@ -281,6 +281,10 @@ lower / upper bounds (`$gt` / `$gte` & `$lt` / `$lte`) according to `Range`
 | `Exists`
 | `findByLocationExists(boolean exists)`
 | `{"location" : {"$exists" : exists }}`
+
+| `IgnoreCase`
+| `findByUsernameIgnoreCase(String username)`
+| `{"username" : {"$regex" : "^username$", "$options" : "i" }}`
 |===
 
 NOTE: If the property criterion compares a document, the order of the fields and exact equality in the document matters.