Mk/Uses/cargo.mk: Add GitLab support and drop CARGO_GH_CARGOTOML

• Add a CARGO_USE_GITHUB equivalent for GitLab instances, CARGO_USE_GITLAB
• Replace CARGO_GH_CARGOTOML with a ${FIND} and just patch all Cargo.toml under ${WRKDIR}. It is too tedious to find all the Cargo.toml that need patching manually due to transitive dependencies.