This makes the first `codeql_pack` in a package add an `installer` target
aliasing the `<name>-installer` one. This makes it so that one can for
example do `bazel run //rust:installer` instead of the stuttering
`bazel run //rust:rust-installer`. If a bazel package defines multiple
`codeql_pack` targets, the first one only will get the `installer` alias.
