linux scripts: Respect $CARGO_TARGET_DIR (#13830)

https://doc.rust-lang.org/cargo/reference/environment-variables.html

Some people (myself included) set this variable to have a single
directory to clean up (or whatever reason one might have for having a
single `target` directory). This changes the linux scripts to respect
that

Release Notes:

- N/A

script/install-linux

@@ -22,5 +22,5 @@ if  [[ "$ZED_CHANNEL" == "dev" ]]; then
 else
   archive="zed-${target}.tar.gz"
 fi
-export ZED_BUNDLE_PATH="target/release/${archive}"
+export ZED_BUNDLE_PATH="${CARGO_TARGET_DIR:-target}/release/${archive}"
 script/install.sh