shore-config - executor configuration used to initialize and configure the underlying client

## Summary

Original Author: @dkirillov

Currently, there's only the Spinnaker Executor/`Backend`. For it to function the (Spinnaker) gate client needs to be properly initialized.

The configuration for the executor is in the shore config under the following path `executor.config.[executor-config-name]`. It could be an object or it could be a file path, it needs to be loaded, and `spinGate.GatewayClient` for the Spinnaker Executor/`Backend` needs to use this configuration.

## Motivation

## Describe alternatives you've considered

## Additional context

Start at the executor.config.[executor-config-name] configuration path and the Spinnaker Executor/Backend entry point, then trace how spinGate.GatewayClient is initialized. Determine how the executor configuration is loaded when it is an object or a file path. Done means the loaded configuration is used to initialize and configure the underlying client.

Written by the indexing model from the issue text.