feat: Add Display/FromStr to ColorChoice

This matches up with `clap_complete::Shell`.  This makes it a bit more flexible.

src/util/color.rs

@@ -64,6 +64,28 @@ impl Default for ColorChoice {
     }
 }
 
+impl std::fmt::Display for ColorChoice {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        self.to_possible_value()
+            .expect("no values are skipped")
+            .get_name()
+            .fmt(f)
+    }
+}
+
+impl std::str::FromStr for ColorChoice {
+    type Err = String;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        for variant in Self::value_variants() {
+            if variant.to_possible_value().unwrap().matches(s, false) {
+                return Ok(*variant);
+            }
+        }
+        Err(format!("Invalid variant: {}", s))
+    }
+}
+
 impl ValueEnum for ColorChoice {
     fn value_variants<'a>() -> &'a [Self] {
         &[Self::Auto, Self::Always, Self::Never]