feat: add an attr to rust_binary for customization of the binary name (#2970)

It's often desirable to set the name of the resulting binary to
something else other than the target name (`attr.name`), perhaps when
the `rust_binary` target is wrapped in a macro, and not considered the
"main" target of that macro.

This diff adds a new `binary_name` attribute to `rust_binary`, which
when set will be used as the resulting binaries prefix instead of the
targets name. The default is to still use the target name.