[red-knot] Resolve Options to Settings (#16000)

## Summary

This PR generalize the idea that we may want to emit diagnostics for 
invalid or incompatible configuration values similar to how we already 
do it for `rules`. 

This PR introduces a new `Settings` struct that is similar to `Options`
but, unlike
`Options`, are fields have their default values filled in and they use a
representation optimized for reads.

The diagnostics created during loading the `Settings` are stored on the
`Project` so that we can emit them when calling `check`.

The motivation for this work is that it simplifies adding new settings.
That's also why I went ahead and added the `terminal.error-on-warning`
setting to demonstrate how new settings are added.

## Test Plan

Existing tests, new CLI test.

crates/ruff_graph/src/db.rs

@@ -79,8 +79,8 @@ impl Db for ModuleDb {
         !file.path(self).is_vendored_path()
     }
 
-    fn rule_selection(&self) -> &RuleSelection {
-        &self.rule_selection
+    fn rule_selection(&self) -> Arc<RuleSelection> {
+        self.rule_selection.clone()
     }
 
     fn lint_registry(&self) -> &LintRegistry {