Allow Templating in Rules

[dallinb]

Templates may be repetitive, but the differences may be environmental. Therefore it makes sense to be able to template rules. For example, if a rule looks like this:

{ "destination_namespaces": "", "destination_topics": "", "jmespath": "country", "regexp": "^{ISO_3166_1_ALPHA_2}$", "source_subscription": "test", "source_topic": "topic.1"}

and there was an environment variable set called ISO_3166_1_ALPHA_2 that was set to FR then the resulting rule would be:

{ "destination_namespaces": "", "destination_topics": "", "jmespath": "country", "regexp": "^FR$", "source_subscription": "test", "source_topic": "topic.1"}