Fixing app creation timing issue

[arschles]

As said in #60, when the operator starts up an app, there's a race between KEDA and the scaler. If the scaler isn't listening for connections by the time KEDA tries to establish one, KEDA will start retrying with an exponential backoff (see this code for example). In this case, depending on how long it takes the scaler to begin listening for connections, KEDA may not retry for a relatively long time, while meanwhile the app is not autoscaling.

This PR ensures that the scaler is ready to accept connections before creating the ScaledObject and instructing KEDA to begin establishing a connection(s)

Checklist

• Commits are signed with Developer Certificate of Origin (DCO)
• Implement readiness/liveness check endpoints on the scaler
• Build tests for these checks
• Make the operator create the scaler deployment with readiness/liveness checks
• Ensure that waitForScaler checks that the scaler is ready according to liveness/readiness checks
• A PR is opened to update the documentation on our docs repo

Fixes #60