Refactor canary auto-generation cli semantics

[marc-1010]

Issue #, if available:

Description of changes:

• Canary auto generation will be disabled for empty canary settings. This is intended to prevent auto generation when a key is added to the .rpdk-config when providers are upgrading their rpdk version set.
• Add an argument local-code-generation to the cfn generate command to enable canary auto generation. This intended to restrict canary autogeneration to specific development use cases. Canary auto-generation should not occur for remote builds.

Unit Test Cases:

• Canary autogeneration will not occur if the local-code-generation flag is missing or False.
• Add local-code-generation=True to existing unit tests

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[ammokhov]

I am confused what benefits we get from having local-code-generation

[marc-1010]

I am confused what benefits we get from having local-code-generation

There is no valid use case/need for re-generating canary code during remote builds. Canaries are not assumed to be a build time generated-source. This cli argument will prevent remote builds from re-generation/overriding canary code during remote host build time. I don't think the burden should be on providers to manually to disable canary generation completely in .rpdk-config to prevent behavior that is unnecessary.