Implement Savepoints and required metadata timeline (#86)

- Introduce avro to save clean metadata with details about the last commit that was retained
- Save rollback metadata in the meta timeline
- Create savepoint metadata and add API to createSavepoint, deleteSavepoint and rollbackToSavepoint
- Savepointed commit should not be rolledback or cleaned or archived
- introduce cli commands to show, create and rollback to savepoints
- Write unit tests to test savepoints and rollbackToSavepoints

hoodie-common/src/main/avro/HoodieCleanMetadata.avsc

@@ -0,0 +1,24 @@
+{"namespace": "com.uber.hoodie.avro.model",
+ "type": "record",
+ "name": "HoodieCleanMetadata",
+ "fields": [
+     {"name": "startCleanTime", "type": "string"},
+     {"name": "timeTakenInMillis", "type": "long"},
+     {"name": "totalFilesDeleted", "type": "int"},
+     {"name": "earliestCommitToRetain", "type": "string"},
+     {"name": "partitionMetadata", "type": {
+     "type" : "map", "values" : {
+        "type": "record",
+        "name": "HoodieCleanPartitionMetadata",
+        "fields": [
+            {"name": "partitionPath", "type": "string"},
+            {"name": "policy", "type": "string"},
+            {"name": "deletePathPatterns", "type": {"type": "array", "items": "string"}},
+            {"name": "successDeleteFiles", "type": {"type": "array", "items": "string"}},
+            {"name": "failedDeleteFiles", "type": {"type": "array", "items": "string"}}
+        ]
+     }
+     }
+     }
+ ]
+}

hoodie-common/src/main/avro/HoodieRollbackMetadata.avsc

@@ -0,0 +1,22 @@
+{"namespace": "com.uber.hoodie.avro.model",
+ "type": "record",
+ "name": "HoodieRollbackMetadata",
+ "fields": [
+     {"name": "startRollbackTime", "type": "string"},
+     {"name": "timeTakenInMillis", "type": "long"},
+     {"name": "totalFilesDeleted", "type": "int"},
+     {"name": "commitsRollback", "type": {"type": "array", "items": "string"}},
+     {"name": "partitionMetadata", "type": {
+     "type" : "map", "values" : {
+        "type": "record",
+        "name": "HoodieRollbackPartitionMetadata",
+        "fields": [
+            {"name": "partitionPath", "type": "string"},
+            {"name": "successDeleteFiles", "type": {"type": "array", "items": "string"}},
+            {"name": "failedDeleteFiles", "type": {"type": "array", "items": "string"}}
+        ]
+     }
+     }
+     }
+ ]
+}

hoodie-common/src/main/avro/HoodieSavePointMetadata.avsc

@@ -0,0 +1,9 @@
+{"namespace": "com.uber.hoodie.avro.model",
+ "type": "record",
+ "name": "HoodieSavepointMetadata",
+ "fields": [
+     {"name": "savepointedBy", "type": "string"},
+     {"name": "savepointedAt", "type": "string"},
+     {"name": "comments", "type": "string"}
+ ]
+}