Add axis label and categories

api/src/engine/models/result/common/chart-axis.model.ts

+import { ObjectType, Field } from '@nestjs/graphql';
+
+@ObjectType()
+export class ChartAxis {
+  @Field({ nullable: true, defaultValue: '' })
+  label?: string;
+
+  @Field(() => [String], { nullable: true, defaultValue: [] })
+  categories: string[];
+}

api/src/engine/models/result/heat-map-result.model.ts

 import { Field, ObjectType } from '@nestjs/graphql';
+import { ChartAxis } from './common/chart-axis.model';
 import { Result } from './common/result.model';
 
 @ObjectType()
@@ -9,9 +10,9 @@ export class HeatMapResult extends Result {
   @Field(() => [[Number]])
   matrix: number[][];
 
-  @Field(() => [String])
-  xLabels: string[];
+  @Field(() => [ChartAxis])
+  xAxis: ChartAxis;
 
-  @Field(() => [String])
-  yLabels: string[];
+  @Field(() => [ChartAxis])
+  yAxis: ChartAxis;
 }