SecurityDefinitions missing "Index" and "IxValue" type family instances

[arjunkathuria]

Hi,

The SecurityDefinitions type defined in the OpenAPI library here

Which is a newtype wrapper over Definitions, which in-turn is a type synonym for an InsOrdHashMap Text type.

SecurityDefinitions seems to be missing type-family instances for Index and IxValue type-families, which enables us to use them with Lenses and refer to their indices using at or ix and set a particular SecurityScheme at that index if needed.

The following instances are already present in the Swagger version of the same data-type here.

Maybe we missed them here. I'll make a PR soon for this.

(Note: They would also need type-class instances for At and Ixed, i'll open a separate issue for that.)