feat(execution): remove spinnaker accounts from execution context

[dbyron-sf]

Add the executions.includeAllowedAccounts flag which defaults to true. If set to true, authentication.allowedAccounts will continue to be populated by accounts in the pipeline execution json. If set to false, the pipeline execution json will show authentication.allowedAccounts = []

Testing notes:
After setting the feature flag to false,

1. Pipelines triggered manually (by clicking play) and automatically (using a service account) continue to run. Pipelines that deploy resources into a kubernetes cluster are still able to do so
2. If the user or service account is unauthorized to run the pipeline, the pipeline will not run

[xibz]

LGTM! One thing I was wondering, but don't have enough context is how useful it would to at least log the amount of allowed accounts. I know fiat, clouddriver, etc do some logging of accounts, but I am unsure if orca does. It would allow for us to ensure that the expected amount is there at least rather than completely missing and may be completely in the dark if there is a lack of logging in orca for this. But that can be a follow up PR since it is really minor

[dbyron-sf]

Yeah, if someone wants that, let's add it in another PR. This seems like a thing where we don't actually need the info, so I'm not sure how helpful it'll be, but I won't stand in the way of logging it if someone wants to.