service to validate Jersey postcodes

[eatyourpeas]

E12 currently still uses findmypostcode.co.uk as a postcode validation and lookup service but RCPCH have more recently moved over to its own instance of postcodes.io. Neither of these support Jersey so a new function is included to validate Jersey postcodes (all of which begin JE) with regex. This won't validate the postcode if it does not exist, but will ensure it is at least more or less in the right format.

Options:

1. stick with our current solution. It is not terrible but not great
2. Use a paid for service. We need to do some due diligence about this beforehand if so, as anecdotally coverage of these services in the Channel Islands in not 100%