Add readiness probes to KEDA/Osiris function app deployment

Sometimes I get 502 on HTTP requests when an app has been scaled to 0. It could be caused by Osiris hitting function app before it's ready. Adding a readiness probe to the function app deployment might help with this.

Start by locating the KEDA/Osiris function app deployment definition in the repository and trace how the deployment is configured. Add the readiness-probe configuration described in the issue, then verify that requests are not sent before the function app is ready and run the relevant deployment tests if present.

Written by the indexing model from the issue text.