doc(operator): Update stackableVersion doc comment

Author: Techassi

crates/stackable-operator/crds/DummyCluster.yaml

@@ -1892,6 +1892,9 @@ spec:
 
                       If not specified, the operator will use its own version, e.g. `26.7.1`. When using a nightly
                       operator or a PR version, it will use the nightly `0.0.0-dev` image.
+
+                      If this is used in combination with `useFloatingTag`, the correct floating tag is computed
+                      automatically, e.g. `26.7.0` becomes `26.7` for the product image.
                     nullable: true
                     type: string
                   useFloatingTag:

crates/stackable-operator/src/commons/product_image_selection.rs

@@ -70,6 +70,9 @@ pub struct AutoProductImage {
     ///
     /// If not specified, the operator will use its own version, e.g. `26.7.1`. When using a nightly
     /// operator or a PR version, it will use the nightly `0.0.0-dev` image.
+    ///
+    /// If this is used in combination with `useFloatingTag`, the correct floating tag is computed
+    /// automatically, e.g. `26.7.0` becomes `26.7` for the product image.
     #[schemars(with = "Option::<String>")]
     stackable_version: Option<semver::Version>,