Documentation: Azure Functions Deployment

[SameerDoshi]

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Adding additional documentation on accessing request headers when dep…loying Apollo Server in an Azure function.

Big picture: Running Apollo in an Azure Function where Apollo access protected backend APIs a user might want to pass a user provided token to the backend API.

[apollo-cla]

@SameerDoshi: Thank you for submitting a pull request! Before we can merge it, you'll need to sign the Apollo Contributor License Agreement here: https://contribute.apollographql.com/

[trevor-scheer]

Going to close this since it's no longer mergeable / we don't have an azure integration that we maintain in this repo anymore. I've captured it in a separate issue here which is concerned with providing getting started guides for serverless applications.