Missing gpgme-json prevents use of popular Mailvelope browser extension

As described at the Mailvelope GitHub repository wiki here <https://github.com/mailvelope/mailvelope/wiki/Mailvelope-GnuPG-integration> users are able to use their local GPG keyring via gpgme-json (rather than the included Openpgp.js library) with several popular webmail services, provided that the gpgme-json binary is available to the browser process. I reviewed the file lists for the binary packages produced from this source package and found no mention of it. Upon closer inspection of the packaging files, the d/rules has an override for dh_missing for the file and a note in the changelog from 2018, but there was no mention of what the circumstances were that necessitated that decision.

If it's possible to correct the conditions that led to the file's exclusion I think it would be well worth pursuing as e-mail becomes evermore commercialized on top of an infrastructure that never did place much of a premium on privacy.

I'm running the dev release of Kubuntu 20.04 LTS "Focal Fossa" with version 1.13.1-7ubuntu2 of the libgpgme11 package.