Webapi-Swagger : Replace locally defined `StdMethod` with the one from Network.HTTP.Types

[kahlil29]

Due to a lack of the Generic typeclass, we have defined an identical StdMethod data types that derives the Generic typeclass. This change has been made in the Network.HTTP.Types package but it may take some time till it is released on hackage/stackage.

Once it is released, we need to import and use it and change the bounds of the relevant package in the webapi-swagger.cabal file.