Feature flag support to turn on/off support for provide-api-key annotation

[chetanmeh]

Enables support for feature flags which for now is used to enable or disable support for provide-api-key (#4284)

Description

With #4284 support was added for provide-api-key annotation. In some cases we may want to enable this feature later. This PR introduces a feature flag support which allow disabling such feature based on config. To disable this feature use config like below

whisk {
    feature-flags {
        require-api-key-annotation = false
    }
}

Related issue and scope

• I opened an issue to propose and discuss this change (#????)

My changes affect the following components

• API
• Controller
• Message Bus (e.g., Kafka)
• Loadbalancer
• Invoker
• Intrinsic actions (e.g., sequences, conductors)
• Data stores (e.g., CouchDB)
• Tests
• Deployment
• CLI
• General tooling
• Documentation

Types of changes

• Bug fix (generally a non-breaking change which closes an issue).
• Enhancement or new feature (adds new functionality).
• Breaking change (a bug fix or enhancement which changes existing behavior).

Checklist:

• I signed an Apache CLA.
• I reviewed the style guides and followed the recommendations (Travis CI will check :).
• I added tests to cover my changes.
• My changes require further changes to the documentation.
• I updated the documentation where necessary.

[rabbah]

i suspect that if this is set to false, some tests will fail.

did you consider also updating this for completeness although there may be another place or two that don't use this method that could be affected.

https://github.com/apache/incubator-openwhisk/blob/fb0bab64de6634725b409a63ffbb90fee295e8c1/tests/src/test/scala/org/apache/openwhisk/core/controller/test/ControllerTestCommon.scala#L88-L95

[chetanmeh]

For now I do not think that we should make test case complex with feature flag support. So test should work assuming all new features enabled (unless using some SPI mechanism). For main code we just validate manually that if feature is disabled then we get back the earlier behavior.

[falkzoll]

This looks great :-). Exactly what I was thinking about. Many thanks for providing this implementation. For me this is a good example and I will take some time and look at the code to understand how it has been implemented. 👍