Add logout request for AD B2C backend

[zahid-arbisoft]

It seems the AzureADB2COAuth2 backend is missing send a sign-out request implementation

API GET https://{tenant}.b2clogin.com/{tenant}.onmicrosoft.com/{policy}/oauth2/v2.0/logout?post_logout_redirect_uri=https%3A%2F%2Fjwt.ms%2F