Default for ENVOY_ADMIN_API

[greatvovan]

I suggest defaulting ENVOY_ADMIN_API to http://localhost:15000 to satisfy the most common case.

[linjmeyer]

I think it's a good suggestion. Right now this env variable being set is what enables Scuttle, that is necessary to ensure things like docker run work for local development outside of a Kubernetes/Istio cluster. Setting this to the default is okay, we just need to add a new environment variable like ENVOY_ADMIN_POLLING=TRUE/FALSE or similar.

[greatvovan]

I see your point, indeed, it is a case, too. But I would prefer to override the default value of ENVOY_ADMIN_API with "" for local runs rather than add it for production. Alternatively we can have SCUTTLE_ENABLED variable defaulting to true.