[Feature request] Parse pgp encrypted blocks

[Artawower]

We need to enhance org-mode-ast to parse a new node: encrypted blocks like this:

-----BEGIN PGP MESSAGE-----

jA0ECQMIjKsa1b+8B6z60kMB/AcxDDxjLdxk0QSPMK/YfsYmHm7GjorsslOTaTlj
UIAFz1Ou89SAAZ5LJ4dAGAYT6xmKTjghKPiNMLWrqmOKO7/D
=Epif
-----END PGP MESSAGE-----

This will allow us to build hidden blocks on the client side with the ability to show sensitive information to the user.