This gets the extensions information for the local service into the snapshot and ExtensionConfigurations for a proxy. It grabs the extensions from config entries and puts them in structs.NodeService.Proxy field, which already is copied into the config snapshot.
Also:
* add EnvoyExtensions to api.AgentService so that it matches structs.NodeService
* extensions: refactor PluginConfiguration into a more generic type
ExtensionConfiguration
Also:
* adds endpoints configuration to lambda golden tests
* uses string constant for builtin/aws/lambda
Co-authored-by: Eric <eric@haberkorn.co>