feat(panel-button): add applet config

This PR adds an optional environment variable to the cosmic-panel-button that allows us to specify how a panel button should present itself (either as 'icon' or as 'text').

The PR also adds the same tracing log that the other applets have, with an initial message notifying that the applet has started.

cosmic-panel-button/src/config.rs

@@ -0,0 +1,44 @@
+use std::collections::HashMap;
+
+use cosmic_config::{cosmic_config_derive::CosmicConfigEntry, CosmicConfigEntry};
+use serde::{Deserialize, Serialize};
+
+#[derive(Debug, Deserialize, Serialize, PartialEq, Clone, CosmicConfigEntry)]
+#[version = 1]
+#[serde(deny_unknown_fields)]
+pub struct CosmicPanelButtonConfig {
+    /// configs indexed by panel name
+    pub configs: HashMap<String, IndividualConfig>,
+}
+
+impl Default for CosmicPanelButtonConfig {
+    fn default() -> Self {
+        Self {
+            configs: HashMap::from([
+                (
+                    "Panel".to_string(),
+                    IndividualConfig {
+                        force_presentation: None,
+                    },
+                ),
+                (
+                    "Dock".to_string(),
+                    IndividualConfig {
+                        force_presentation: Some(Override::Icon),
+                    },
+                ),
+            ]),
+        }
+    }
+}
+
+#[derive(Debug, Deserialize, Serialize, PartialEq, Default, Clone)]
+pub struct IndividualConfig {
+    pub force_presentation: Option<Override>,
+}
+
+#[derive(Debug, PartialEq, Clone, Serialize, Deserialize)]
+pub enum Override {
+    Icon,
+    Text,
+}