Fixing target and adding debug to Rust gitignore (#3436)

The problem here was two fold:
1. the folder "/target/" would be top-level of the repo only, it should be "target/" to properly exclude target folders anywhere in the repo
2. the default Rust/Cargo folder when compiling code is "debug/", which gets used perhaps more often that "target/", added that

Rust.gitignore

 # Generated by Cargo
 # will have compiled files and executables
-/target/
+debug/
+target/
 
 # Remove Cargo.lock from gitignore if creating an executable, leave it for libraries
 # More information here https://doc.rust-lang.org/cargo/guide/cargo-toml-vs-cargo-lock.html