Create v3-upgrade-guide.md (#430)

* Create v3-upgrade-guide.md

* Update v3-upgrade-guide.md

* Added alternatives to ImplicitMsal

Author: nikithauc

changelogs/v3-upgrade-guide.md

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+# Microsoft JavaScript SDK v3 upgrade guide
+
+- [Breaking Changes](#Breaking-Changes)
+- [Enhancements](#Enhancements)
+- [Deprecation](#Deprecation)
+## Breaking Changes
+
+### Supported Node version and TypeScript update
+- Microsoft Graph JS SDK requires Node.js 10 LTS or higher.
+- Updated to TypeScript 4.x.
+
+### LargeFileUploadTask 
+- Modified the `FileObject` interface which now contains the `sliceFile` function. Learn more [LargeFileUploadTask](./docs/tasks/LargeFileUploadTask.md). 
+- The `FileObject` instance passed on creation of the `LargeFileUploadTask` object should contain the implementation of the `sliceFile` function.
+- Added new classes `FileUpload` and `StreamUpload` implementing the `FileObject` interface.
+
+### Removed `timeout` option from `FetchOptions` interface
+- Recommended way is to [cancel a request](./docs/CancellingAHTTPRequest.md) by passing a signal.
+
+### Update in the `package.json` entry points.
+```json
+{
+    "main": "lib/src/index.js",
+    "module": "lib/es/src/index.js",
+    "browser": {
+	    "./lib/es/src/index.js": "./lib/es/src/browser/index.js"
+    }
+}
+```
+## Removed the `graph-es-sdk.js`
+* `graph-es-sdk.js` - the bundled file in ES format will not be shipped anymore as the ES modules are being shipped.
+* `graph-js-sdk.js` will be shipped as is.
+
+## Enhancements
+
+### Introducing support for `@azure/identity TokenCredentials`
+- Added a `TokenCredentialAuthenticationProvider` enabling the use of `@azure/identity` `credential classes` for authentication purposes. 
+- The `TokenCredentialAuthenticationProvider` enables server-side authentication using `credential classes` such as `ClientSecretCredential` or `ClientCertificateCredential`.
+- Find the samples on how to use `TokenCredentialAuthenticationProvider` here - [TokenCredentialAuthenticationProvider samples](./samples/tokenCredentialSamples)
+
+### LargeFileUploadTask
+
+- Added support for Node.js Stream upload. Learn more [LargeFileUploadTask](./docs/tasks/LargeFileUploadTask.md). 
+- Added capabilities to track the upload progress using `UploadEventHandlers`.
+- Resolved a bug to enable large file uploads to Outlook and Print APIs.
+
+### Added `browser` field in package.json.
+- The `browser` field indicates the entry point for client applications using Microsoft Graph JS SDK library.
+
+## Deprecation
+
+### Deprecating `ImplicitMSALAuthenticationProvider` 
+* Use of `ImplicitMSALAuthenticationProvider`, that is,using the implicit authorization flow is not recommended any more. [OAuth 2.0 Implicit Grant](https://oauth.net/2/grant-types/implicit/).
+* Alternatives to `ImplicitMSALAuthenticationProvider` - 
+	* TokenCredentialAuthenticationProvider with the `azure/identity` library. Learn more about [InteractiveBrowserCredential](https://github.com/Azure/azure-sdk-for-js/blob/master/sdk/identity/identity/interactive-browser-credential.md) 
+	* A CustomAuthenticationProvider with an auth library of your choice. [Choose a Microsoft Graph authentication provider based on scenario](https://docs.microsoft.com/en-us/graph/sdks/choose-authentication-providers?tabs=CS)
+