linux: Use optional compile-time RELEASE_VERSION variable (#11490)

This implements `app_version` on Linux by using an optional,
compile-time `RELEASE_VERSION` env var that can be set.

We settled on the `RELEASE_VERSION` as the name, since it's similar to
`RELEASE_CHANNEL` which we use in Zed.

cc @ConradIrwin @mikayla-maki 

Release Notes:

- N/A

Co-authored-by: Bennet <bennetbo@gmx.de>

crates/gpui/src/platform/linux/platform.rs

@@ -348,7 +348,12 @@ impl<P: LinuxClient + 'static> Platform for P {
     }
 
     fn app_version(&self) -> Result<SemanticVersion> {
-        Ok(SemanticVersion::new(1, 0, 0))
+        const VERSION: Option<&str> = option_env!("RELEASE_VERSION");
+        if let Some(version) = VERSION {
+            version.parse()
+        } else {
+            Ok(SemanticVersion::new(1, 0, 0))
+        }
     }
 
     fn app_path(&self) -> Result<PathBuf> {