Lemur: Authenticated low-privilege users can read plaintext destination credentials (SFTP password / private-key passphrase) via the destinations API

Summary Lemur's destination read endpoints -- GET /api/1/destinations and GET /api/1/destinations/ -- return the full set of stored plugin option values to any authenticated user, with no authorization check and no redaction of secret-bearing options. The sibling write endpoints POST/PUT/DELETE a...