A way to encrypt with just a public key

[thasaleni]

Describe the bug
it is normal for third parties to give you a public key to encrypt a file you will send to them, i.e: they don't give you anything else, and the key is not signed. Currently the library requires a recipient address (which if I understand correctly is to search for the public key?) But you don't really need to search as if you are given a public key file you will only have that public key in the file and nothing else.
To Reproduce
Steps to reproduce the behavior (code sample)
Try and encrypt a file with just a unsigned public key, and no recipient address
Expected behavior
A clear and concise description of what you expected to happen.
You should be able to encrypt a file with just the public key as available, official GPG tools can do that without any problem, but if you want to automate that with code this library constrains you

** System (please complete the following information):**

• Device: [e.g. iPhone6]
  Lenovo Thinkpad

• OS: [e.g. Linux]
  Windows 10

• Java [output of java -version]
  java version "1.8.0_231"
  Java(TM) SE Runtime Environment (build 1.8.0_231-b11)
  Java HotSpot(TM) 64-Bit Server VM (build 25.231-b11, mixed mode)

• Version [e.g. 2.2.0]
  2.2.0
  Additional context
  Add any other context about the problem here.

[ispringer]

See also #27, which I think would also cover this issue.