Provide fix for MM chart wait.sh script hardcoded namespace

Summary

mattermost wait.sh script checks hard coded mattermost namespace for instance of Mattermost CR.

Update script to dynamically call kube api for namespace based on the pod's deployment namespace

Steps to reproduce

Deploy mattermost to a different namespace

What is the current behavior?

Deploy mattermost to a different namespace and wait.sh fails due to hardcoded ns.

What is the expected behavior?

wait script should succeed in any ns

Relevant logs and/or screenshots

PB thread https://chat.il4.dso.mil/platform-one/pl/yj3m7jmouinhb8tuhgtrstjd3y

Possible fixes

provided

/cc {put CODEOWNERs @githandles here}