[storage] add convenience methods exists, createIfNotExists, deleteIfExists (Azure#8964)

* [storage-blob] add CreateIfNotExists and DeleteIfExists for Container and Blob

* [storage-flie-share] add CreateIfNotExists and DeleteIfExists

* restore package.json

* [storage-queue] add createIfNotExists and deleteIfExists

* add exists for storage-file-share

* add createIfNotExists and deleteIfExists for storage-file-datalake

* record tests

* fix typo

* change return type - blob

* change return type - datalake

* change return type - file

* change return type - queue

Co-authored-by: Lin Jian <[email protected]>

Author: ljian3377

sdk/storage/storage-blob/CHANGELOG.md

@@ -1,5 +1,10 @@
 # Release History
 
+## 12.2.0 (unreleased)
+
+- Added convenience method `createIfNotExists` for `ContainerClient`, `AppendBlobClient` and `PageBlobClient`.
+- Added convenience method `deleteIfExists` for `ContainerClient` and `BlobClients`.
+
 ## 12.1.2 (2020.05)
 
 - Fix data corruption failure error [issue #6411](https://github.com/Azure/azure-sdk-for-js/issues/6411) when downloading compressed files. [PR #7993](https://github.com/Azure/azure-sdk-for-js/pull/7993)