refactor 'latest_release' and address PR feedback

rust/stackable-cockpit/src/platform/release/spec.rs

@@ -130,6 +130,11 @@ impl ReleaseSpec {
 }
 
 impl ReleaseList {
+    /// Checks if a value provided in the '--release' argument is in the release list
+    pub fn contains(&self, release: &str) -> bool {
+        self.inner().contains_key(release)
+    }
+
     /// Retrieves the latest release from the list and applies a sanity check to the release format.
     pub fn latest_release(&self) -> Result<String, Error> {
         let release = self.inner().first().context(EmptyReleaseListSnafu)?.0;

rust/stackablectl/src/cmds/demo.rs

@@ -173,6 +173,9 @@ impl DemoArgs {
 
         let release_branch = match &self.release {
             Some(release) => {
+                if !release_list.contains(release) {
+                    return NoSuchReleaseSnafu { name: release }.fail();
+                }
                 if release == "dev" {
                     "main".to_string()
                 } else {

rust/stackablectl/src/cmds/stack.rs

@@ -120,6 +120,9 @@ pub enum CmdError {
     #[snafu(display("failed to serialize JSON output"))]
     SerializeJsonOutput { source: serde_json::Error },
 
+    #[snafu(display("no release with name '{name}'"))]
+    NoSuchRelease { name: String },
+
     #[snafu(display("failed to get latest release"))]
     LatestRelease { source: platform::release::Error },
 
@@ -155,6 +158,9 @@ impl StackArgs {
 
         let release_branch = match &self.release {
             Some(release) => {
+                if !release_list.contains(release) {
+                    return NoSuchReleaseSnafu { name: release }.fail();
+                }
                 if release == "dev" {
                     "main".to_string()
                 } else {