S3 backend for storage service (#1629)

Co-authored-by: Alok Kumar <rajalokan@gmail.com>

charts/fission-core/values.yaml

@@ -110,11 +110,23 @@ router:
 
 ## Persist data to a persistent volume.
 persistence:
-  ## If true, fission will create/use a Persistent Volume Claim
+  ## If true, fission will create/use a Persistent Volume Claim unless storageType is set to s3
   ## If false, use emptyDir
   ##
   enabled: true
 
+  ## Must be set to either local or S3.
+  ## If storateType is set(other than local), one of its backend configuration must be set as below.
+  #storageType: local | s3
+
+  ## Sample configruation for AWS s3 storage backend
+  #s3:
+  # bucketName: <awsBucketName>
+  # subDir: <sub directory within a bucket>
+  # accessKeyId: <awsAccessKeyId>
+  # secretAccessKey: <awsSecretAccessKey>
+  # region: <awsRegion>
+
   ## A manually managed Persistent Volume Claim name
   ## Requires persistence.enabled: true
   ## If defined, PVC must be created manually before volume will be bound