fix: support multiple SSHPubKey records per user

There was one blazing issue with the previous implementation regardless
of the multiple records: we were generating fingerprints by storing
the key into a file and reading it with ssh-keygen. This is absolutely
terrible and was not meant to be left around (it was forgotten, my bad).

Took this opportunity to clean up a few things:
- simplify pubkey validation
- centralize things a bit better

Signed-off-by: Kevin Morris <kevr@0cost.org>

test/test_user.py

@@ -183,14 +183,14 @@ def test_user_has_credential(user: User):
 
 
 def test_user_ssh_pub_key(user: User):
-    assert user.ssh_pub_key is None
+    assert user.ssh_pub_keys.first() is None
 
     with db.begin():
         ssh_pub_key = db.create(SSHPubKey, UserID=user.ID,
                                 Fingerprint="testFingerprint",
                                 PubKey="testPubKey")
 
-    assert user.ssh_pub_key == ssh_pub_key
+    assert user.ssh_pub_keys.first() == ssh_pub_key
 
 
 def test_user_credential_types(user: User):