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>

script/bundle-linux

@@ -26,7 +26,11 @@ done
 export ZED_BUNDLE=true
 
 channel=$(<crates/zed/RELEASE_CHANNEL)
+
 version="$(cargo metadata --no-deps --manifest-path crates/zed/Cargo.toml --offline --format-version=1 | jq -r '.packages | map(select(.name == "zed"))[0].version')"
+# Set RELEASE_VERSION so it's compiled into GPUI and it knows about the version.
+export RELEASE_VERSION="${version}"
+
 commit=$(git rev-parse HEAD | cut -c 1-7)
 
 version_info=$(rustc --version --verbose)