Apply bnd plugin to generate OSGI bundle metadata

[badfish69]

A trivial change to enable/configure the BND plugin.
This allows the generation of OSGI bundle metadata in the resulting jar file, which in turn resolves classloader issues when running bouncy-gpg in OSGI environments.

[neuhalje]

I‘ll give it a shot this weekend. If it works I can do a release. Is there anything else to do/needed for osgi integration?

Could you maybe add a README.osgi.md file with some examples and instructions? Nothing fancy.

[badfish69]

Regarding OSGI integration, no there is nothing special required. All we're aiming to do here is ensure that the packaged jar file contains the metadata which is used by the OSGI framework to manage inter-bundle class dependencies.
I'm not sure what I could put in a README file that will help here. Anyone who is using this package in an OSGI environment should already know how to do it (specifics are dependent on chosen build system and target OSGI implementation).

[neuhalje]

release/v2.1.2 released

Thanks a lot for your contribution, @badfish69 !