Add backupStats func to docs (#358)

docs/functions.rst

@@ -829,6 +829,63 @@ Example:
       namespace: "{{ .Deployment.Namespace }}"
       snapshots: "{{ .ArtifactsIn.backupInfo.KeyValue.manifest }}"
 
+BackupDataStats
+---------------
+
+This function get stats for the backed up data from the object store location
+
+.. note::
+   It is important that the application includes a ``kanister-tools``
+   sidecar container. This sidecar is necessary to run the
+   tools that get the information from the object store.
+
+Arguments:
+
+.. csv-table::
+   :header: "Argument", "Required", "Type", "Description"
+   :align: left
+   :widths: 5,5,5,15
+
+   `namespace`, Yes, `string`, namespace in which to execute
+   `backupArtifactPrefix`, Yes, `string`, path to the object store location
+   `backupID`, Yes, `string`, unique snapshot id generated during backup
+   `mode`, No, `string`, mode in which stats are expected
+   `encryptionKey`, No, `string`, encryption key to be used for backups
+
+Outputs:
+
+.. csv-table::
+   :header: "Output", "Type", "Description"
+   :align: left
+   :widths: 5,5,15
+
+   `mode`,`string`, mode of the output stats
+   `fileCount`,`string`, number of files in backup
+   `size`, `string`, size of the number of files in backup
+
+Example:
+
+.. code-block:: yaml
+  :linenos:
+
+  actions:
+    backupStats:
+      type: Deployment
+      outputArtifacts:
+        backupStats:
+          keyValue:
+            mode: "{{ .Phases.backupDataStatsFromObjectStore.Output.BackupDataStatsOutputMode }}"
+            fileCount "{{ .Phases.backupDataStatsFromObjectStore.Output.BackupDataStatsOutputFileCount }}"
+            size: "{{ .Phases.backupDataStatsFromObjectStore.Output.BackupDataStatsOutputSize }}"
+      phases:
+        - func: BackupData
+          name: BackupToObjectStore
+          args:
+            namespace: "{{ .Deployment.Namespace }}"
+            backupArtifactPrefix: s3-bucket/path/artifactPrefix
+            mode: restore-size
+            backupID: "{{ .ArtifactsIn.snapshot.KeyValue.backupIdentifier }}"
+
 
 Registering Functions
 ---------------------