Change products.core to lowercase "self-hosted"

Formerly, this variable was capitalized as "Self-Hosted" which could be
confusing since it implied the term was a proper noun. However, it is
not. There is no such Product Name (tm), it's just an adjective
referring to the deployment model.

Related to DOC-10665

src/current/_data/products.yml

@@ -4,7 +4,7 @@ dedicated: Dedicated
 
 dedicated-advanced: Dedicated advanced
 
-core: Self-Hosted
+core: self-hosted
 
 enterprise: Enterprise