Add a `version` command to probe the ai controller workloads version

[adhityaravi]

Description:

The envoy controller itself provides a command to fetch the version of the deployed controller workload - envoy-gateway version

But there is no equivalent for the ai-gateway workload. We are trying to automate the deployment and management of the the ai-gateway as a juju charm and having a similar version command or a reliable way to probe the version from the ai gateway controller application would help us sync the versions of the ai-gateway and the the extproc images more reliably.

Relevant downstream issue: canonical/service-mesh#126