Need support for mutually exclusive / multi-way settings

**What problem does this solve?**

Currently a rule can only be enabled or disabled.
But some rules come in pairs: [`OxfordComma`](harper-core/src/linting/oxford_comma.rs) / [`NoOxfordComma`](harper-core/src/linting/no_oxford_comma.rs)

Others in PR or draft PR aim to allow the user to prefer one side or another:
- https://github.com/Automattic/harper/pull/2209

Or a three-way choice between preferring one vs the other vs not caring:
- https://github.com/Automattic/harper/pull/2384

**Proposed Solution**

There's a small discussion: https://github.com/Automattic/harper/discussions/2208
But more is needed.
- An extension to `LintGroup`?
- One or more additional kinds of group besides `LintGroup`?
- Additions to the config/settings/prefs that provide a place for the user to choose.

**Component**
- [x] Core engine
- [ ] Plugin/Extension
- [ ] Other: _____

Start by reading the linked discussion and the existing OxfordComma and NoOxfordComma implementations in harper-core/src/linting/oxford_comma.rs and harper-core/src/linting/no_oxford_comma.rs. Review PRs 2209 and 2384, then define how LintGroup or another grouping mechanism and the config/settings/prefs should represent mutually exclusive choices, with those preference scenarios supported as the completion criteria.

Written by the indexing model from the issue text.