Allow a bunch of elasticache actions for CI testing elasticache module

[stefanhorning]

Needed for PR ansible-collections/community.aws#410

[markuman]

LGTM

[jillr]

Hi @stefanhorning, the policies here look good but we'll also need a new terminator class for Elasicache since this is a new service being enabled in CI. There are some examples here: https://github.com/mattclay/aws-terminator/blob/master/aws/terminator/data_services.py

[stefanhorning]

@jillr Done now. I hope I guessed the purpose of the methods correctly from the other examples.

[jillr]

There's a few more permissions needed here, and it turns out CacheClusterCreateTime isn't available until CacheClusterStatus is available so the terminator class will need to ignore clusters with a pending state. I've got a diff that works with 410 so I'll merge that after this one so you won't be held up any longer.

I didn't fully review your patch @stefanhorning but I'll leave some comments from my testing over there. Thanks for your work on this!

[stefanhorning]

Thanks for pushing this forward!