Create generic PubID gem for auto-parsing PubIDs

[ronaldtse]

We have several PubID implementations that can be tied together:

• https://github.com/metanorma/pubid-nist
• https://github.com/metanorma/pubid-iso
• https://github.com/metanorma/pubid-ieee

As described in https://github.com/metanorma/pubid-ieee/issues/25#issuecomment-1070331364 , we should be able to do this:

expect(PubID::Registry.parse("ISO/IEC 13213")).to be_instance_of PubId::Iso::Identifier
expect(PubID::Registry.parse("IEEE/ANSI Std 484-1987")).to be_instance_of PubId::Ieee::Identifier