Create SET cache endpoint

Cache SET endpoint implementation

Closes #3 (closed) FYI: @tziai @valerii.kalashnikov

design/design.go

@@ -62,6 +62,30 @@ var _ = Service("cache", func() {
 			Response(StatusOK)
 		})
 	})
+
+	Method("Set", func() {
+		Description("Set a JSON value in the cache.")
+
+		Payload(CacheSetRequest)
+		Result(Empty)
+
+		HTTP(func() {
+			POST("/v1/cache")
+
+			Header("key:x-cache-key", String, "Cache entry key", func() {
+				Example("did:web:example.com")
+			})
+			Header("namespace:x-cache-namespace", String, "Cache entry namespace", func() {
+				Example("Login")
+			})
+			Header("scope:x-cache-scope", String, "Cache entry scope", func() {
+				Example("administration")
+			})
+			Body("data")
+
+			Response(StatusCreated)
+		})
+	})
 })
 
 var _ = Service("openapi", func() {