Gracefully handle a missing crypt key in the Query Tool connection endpoints. (#10065)

After a backend/pod restart the in-memory crypt key is gone, so
manager.connection() raises CryptKeyMissing. The new-connection
endpoints (_check_server_connection_status and get_new_connection_*)
swallowed it in a broad "except Exception", logged a full ERROR
traceback, and returned a generic error the client cannot recognise.
The standard recovery (a 503 CRYPTKEY_MISSING response that the client
uses to transparently re-establish the key and retry) therefore never
fired, leaving a spurious "Crypt key is missing" message in the Query
Tool and noisy tracebacks in the log.

Re-raise CryptKeyMissing (along with ConnectionLost /
SSHTunnelConnectionLost) before the generic handler, matching the
pattern already used by the query execution path, so these endpoints
emit the standard CRYPTKEY_MISSING response and the client recovers
gracefully.

Closes #10027