kibana-proxy CrashLoopBackoff with error Invalid configuration cookie_secret must be 16, 24, or 32 bytes to create an AES cipher

* Before this update, the `kibana-proxy` Pod sometimes entered the `CrashLoopBackoff` state and logged the following message `Invalid configuration: cookie_secret must be 16, 24, or 32 bytes to create an AES cipher when pass_access_token == true or cookie_refresh != 0, but is 29 bytes.` The exact actual number of bytes could vary. With this update, generation of the Kibana session secret has been corrected, and the kibana-proxy Pod no longer crash loops due to this error.