Develop a common application interface

# ✨ Feature Request

We should have a common application interface for use across ANTS and Contrib to facilitate development of ancillary science and core applications.

## Requirements

The application interface should be consistent with UG-ANTS: in principle it could live in a separate grid-independent package.
See https://github.com/MetOffice/UG-ANTS/issues/57

## Context

Potentially this could replace or tie in a few parts of the existing ANTS code:

- The `AntsArgParser`
- The global `Config` object
- The logging framework

Start by reviewing the existing AntsArgParser, global Config object, and logging framework, then compare the intended interface with UG-ANTS issue 57. Clarify whether the common interface should be a separate grid-independent package and how it would replace or connect these components. Done means the interface scope and integration path are agreed for ANTS, Contrib, and ancillary applications.

Written by the indexing model from the issue text.