Check for all required env vars

We are using `require-env-variable` to ensure certain environment
variables are properly set on service start.  This adds in a few more
required variables. Even though they are not directly passed into our
service classes, they are used by third party libraries and so we want
to ensure their existence.

src/server.ts

@@ -17,6 +17,9 @@ const {
   FUSION_AUTH_SFTP_CLIENT_ID,
   FUSION_AUTH_SFTP_CLIENT_SECRET,
 } = requireEnv(
+  'FUSION_AUTH_HOST',
+  'FUSION_AUTH_KEY',
+  'PERMANENT_API_BASE_PATH',
   'SSH_HOST_KEY_PATH',
   'FUSION_AUTH_SFTP_APP_ID',
   'FUSION_AUTH_SFTP_CLIENT_ID',