*info functions should validate vpu argument

`nhdR::nhd_plus_info(vpu = "03", component = "NHDPlusAttributes")` should return an error:

> 03 is not a valid vpu. Are you missing a letter designation? See VPU map.

This error is thrown when running the equivalent *load function:

`nhdR::nhd_plus_load(vpu = "03", component = "NHDPlusAttributes", dsn = "PlusWaterbodyLakeMorphology")`