Handle HTTP requests when token is being refreshed

[DonOmalVindula]

Describe the issue:
Currently we have implemented the httpRequest method to automatically refresh the token when a 401 status is encountered. But we do not have a method to block the HTTP requests when the token is being refreshed and this can lead to failures as the SDK will attempt to refresh the token again while it is already being refreshed.

We need an approach to block the HTTP requests until the token is refreshed and then retry the failed HTTP calls with the newly refreshed token. We have done a similar approach for SDK 0.4.xx versions. But we have missed this implementation on later versions.

• Fix retry logic #149
• Add logic to gracefully retry 401 error #148

How to reproduce:

1. Wait until access token is expired.
2. Simultaneously send multiple HTTP calls via httpRequest() method
3. You will see that certain calls will fail along with the token refresh call as they are attempt to refresh the token multiple times simultaneously.

Expected behavior:

1. When a 401 is encountered first, send a single refresh token call
2. Block all the other calls while token in being refreshed
3. Once the token has finished refreshing, attempt the blocked calls with the newly obtained token

Environment information (Please complete the following information; remove any unnecessary fields) :

• Product Version: [e.g., IS 5.10.0, IS 5.9.0]
• OS: [e.g., Windows, Linux, Mac]
• Browser: [e.g., Chrome, Firefox]
• SDK Version: [e.g., 0.1.0, 0.1.1]