Rule S6422: Calls to "async" methods should not be blocking in Azure Functions

[andrei-epure-sonarsource]

MMF: https://jira.sonarsource.com/browse/MMF-2699

RSPEC PR to be merged after implementing this ticket: SonarSource/rspec#957

• See implementation for Rule S4462 (CallToAsyncMethodShouldNotBeBlocking).
• This ticket should also modify S4462 to not raise on Azure Functions - modification to the S4462 RSPEC to add as exception Modify rule S4462: add exception for Azure Functions rspec#967
• Probably the same implementation in CallToAsyncMethodShouldNotBeBlocking can be used for both, and raise S6422 or S4462 depending on the context.