cloud: add endpoint resolvers for az based access

[ss89]

Given one uses the vpc endpoint interfaces of aws services and multiple AZs for instances hosting a gosoline based app, you might want to access the aws service in the same AZ your instance is in.
That is to save costs which would occurr when routing to another AZ.
For that i'd need to resolve the metadata and add an endpoint resolver.

[ss89]

@j4k4 would that be viable to you? I couldn't figure out an out-of-the-box working infrastructure solution that wouldn't require application level changes.