* DB migration adds app_versions table for managing known app versions.
* /ping reads app version from User-Agent header and responds with latest version if the app is OKO and its version is older than the latest one stored.
* Added endpoint /app-versions which
* lists all known versions via GET
* adds/updates a version via POST
#3Fix#4
* Go version set to 1.19 in go.mod.
* Alpine upgraded to 3.16 in Dockerfile.
* DB restart checkpoint is forced manually after 15 mins of inactivity.
* DB truncate checkpoint is forced manually at exit.