feat: adopt v2 config_overrides; build against the smooth-operator branch

Patches operator-rs to the smooth-operator branch (matching trino- and
hdfs-operator) and actually consumes it: AirflowConfigOverrides.webserver_config_py
now uses stackable_operator::v2::config_overrides::KeyValueConfigOverrides — the
Merge-capable variant trino/hdfs use — instead of the v1 type. Drops the v1
KeyValueOverridesProvider impl and the as_product_config_overrides() call;
merged_overrides reads the override map directly (role <- role-group extend), so
the rendered webserver_config.py is unchanged (39 tests pass).

The CRD gains `nullable: true` on the webserver_config.py override values (v2
allows null to delete a key). Regenerated extra/crds.yaml, Cargo.nix, and
crate-hashes.json.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: adwk67

Cargo.lock

@@ -33,5 +33,6 @@ tokio = { version = "1.40", features = ["full"] }
 tracing = "0.1"
 
 [patch."https://github.com/stackabletech/operator-rs.git"]
+stackable-operator = { git = "https://github.com/stackabletech//operator-rs.git", branch = "smooth-operator" }
 # stackable-operator = { git = "https://github.com/stackabletech//operator-rs.git", branch = "main" }
 # stackable-operator = { path = "../operator-rs/crates/stackable-operator" }