fix: group all server options under Server Options help heading

The --server-password, --server-password-hash, --server-username,
--server-jwt-secret, --server-jwt-secret-file, and --server-max-body-size
options were appearing in the generic Options section instead of the
Server Options section.

Dockerfile

@@ -64,4 +64,4 @@ ENV KEEP_SERVER_PORT=21080
 # ENV KEEP_CLIENT_PASSWORD=""
 # ENV KEEP_CLIENT_JWT=""
 
-ENTRYPOINT ["/keep"]
+ENTRYPOINT ["/keep", "--server"]