feat: add key value pair (#117)

Author: GurtejSohi

hypertrace-core-graphql-common-schema/src/main/java/org/hypertrace/core/graphql/common/schema/pair/KeyValuePair.java

@@ -0,0 +1,27 @@
+package org.hypertrace.core.graphql.common.schema.pair;
+
+import graphql.annotations.annotationTypes.GraphQLDescription;
+import graphql.annotations.annotationTypes.GraphQLField;
+import graphql.annotations.annotationTypes.GraphQLName;
+import graphql.annotations.annotationTypes.GraphQLNonNull;
+
+@GraphQLName(KeyValuePair.TYPE_NAME)
+@GraphQLDescription("A pair of a key and a value")
+public interface KeyValuePair {
+  String TYPE_NAME = "KeyValuePair";
+
+  String KEY = "key";
+  String VALUE = "value";
+
+  @GraphQLField
+  @GraphQLName(KEY)
+  @GraphQLNonNull
+  @GraphQLDescription("String based key name")
+  String key();
+
+  @GraphQLField
+  @GraphQLName(VALUE)
+  @GraphQLNonNull
+  @GraphQLDescription("Value of a generic type")
+  Object value();
+}