Error when packaging when Lambdas and cirrus-lib have duplicated requirements

[jkeifer]

With the way that we now inject the locally-install cirrus-lib and extend lambda requirements with those of cirrus-lib, it is possible that we end up with duplicate specifications for a requirement when it is required by both the lambda and cirrus-lib.

How to solve this problem is less than straightforward. If only we could pip install cirrus-lib from the local env then pip could resolve these requirements issues for us, but that alone doesn't really work. I do wonder though if we could import something from pip that would resolve the set of dependencies we need based on those listed. Trying to roll that ourselves sounds painful and rife with risk.

Until we have a solution to this issue, users that encounter an error about duplicate requirements will need to remove/comment out the duplicated requirement(s) in the affected lambda definitions(s).

[jkeifer]

Let's detect this situation and raise an error that points to this issue or something.