Change footprint variabel from bool to string

The footprint variable also indicates the type of statistic used now

pkg/archive/testdata/archive/alex/cluster.json

@@ -8,7 +8,7 @@
       },
       "scope": "node",
       "aggregation": "avg",
-      "footprint": true,
+      "footprint": "avg",
       "timestep": 60,
       "peak": 128,
       "normal": 128,
@@ -36,7 +36,7 @@
       },
       "scope": "node",
       "aggregation": "sum",
-      "footprint": true,
+      "footprint": "max",
       "timestep": 60,
       "peak": 512,
       "normal": 128,
@@ -51,7 +51,7 @@
       },
       "scope": "hwthread",
       "aggregation": "sum",
-      "footprint": true,
+      "footprint": "avg",
       "timestep": 60,
       "peak": 9216,
       "normal": 1000,
@@ -66,7 +66,7 @@
       },
       "scope": "socket",
       "aggregation": "sum",
-      "footprint": true,
+      "footprint": "avg",
       "timestep": 60,
       "peak": 350,
       "normal": 100,
@@ -108,7 +108,7 @@
       },
       "scope": "accelerator",
       "aggregation": "avg",
-      "footprint": true,
+      "footprint": "avg",
       "timestep": 60,
       "peak": 100,
       "normal": 80,