Add FRRNAField

[babastienne]

Added FRRNAField to allow the use of RNA French Association Identification Number. More information on https://fr.wikipedia.org/wiki/R%C3%A9pertoire_national_des_associations or https://www.associations.gouv.fr/le-rna-repertoire-national-des-associations.html

All Changes

• [x] Add an entry to the docs/changelog.rst describing the change.

• [x] Add an entry for your name in the docs/authors.rst file if it's not already there.

New Fields Only

• [x] Prefix the country code to all fields.

• [x] Field names should be easily understood by developers from the target localflavor country. This means that English translations are usually not the best name unless it's for something standard like postal code, tax / VAT ID etc.

• [x] Add meaningful tests. 100% test coverage is not required but all validation edge cases should be covered.

• [x] Add .. versionadded:: <next-version> comment markers to new localflavors.

• [x] Add documentation for all fields.

[benkonrath]

Thanks for the PR. Sorry for the delay in merging it.