Flag up an issue if a secret specified by a function isn't available

[alexellis]

Expected Behaviour

Flag up an issue if a secret specified by a function isn't available

Current Behaviour

There is an error in the logs, however, in a recent support case, the error was somehow missed.

Possible Solution

Flag up with a red check mark in the generated report i.e. where we also mention readOnlyFilesystem etc.

Steps to Reproduce (for bugs)

1. Deploy a function that references a secret
2. Make sure that secret doesn't exist.