Add appversion to renovate updates

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. When deployed, this allows us to use helm list to get the app version for all Big Bang components.

In this repo, the Chart.yaml is inaccurate.

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