tests/smime: Include the Sample LAMPS Certificate Authority

This CA is useful for test suites and the like, but is not an
actually-secure CA, because its secret key material is also published.

I plan to use it for its intended purpose in the notmuch test suite.

It was copied from this Internet Draft:

https://tools.ietf.org/id/draft-dkg-lamps-samples-01.html#name-certificate-authority-certi

Signed-off-by: Daniel Kahn Gillmor <dkg@fifthhorseman.net>