Add appversion to Chart.yaml and renovate

Add appversion to Chart.yaml so that helm list will return the correct application version. This field will likely be used by bbctl in the future.

In Chart.yaml, appversion should be kept in sync with the version of the image being pulled. Have renovate automatically check and update appversion against the image version.

Example: https://repo1.dso.mil/platform-one/big-bang/apps/developer-tools/gitlab/-/blob/main/renovate.json#L18-25