Add entrypoint for app-level code

[ejizba]

UPDATE: Per the final design, you can specify a single file or a glob pattern for multiple files as the "main" field in your "package.json" file.

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Basically, provide a way for users to run app-level code when the worker is initialized. This would be directly beneficial for the new hooks feature (#522), but could realistically be used for any arbitrary code. Current proposal is to respect the main field in a user's package.json

NOTE: I already added the function app dir to the worker init request in Azure/azure-functions-host#8144, necessary to read the user's package.json

[aaronpowell]

With the change on the Function Host, will there be some more data provided to the workers when they start up, info that can be used to find the package.json?

[ejizba]

Yes that is the point of the change on the host and it will also help with #531, if that's what you're after 😝

[aaronpowell]

Yes that is the point of the change on the host and it will also help with #531, if that's what you're after 😝