Application Versioning

[kraftp]

The PR expands the notion of application versions, which were previously only used in DBOS Cloud, to support more robust self-hosting of DBOS applications.

• When DBOS is launched, it constructs an application version by hashing the source of the application's workflows. This version is stable across restarts, but changes if the application's code is changed.
• The application version can be overridden through the DBOS__APPVERSION environment variable.
• When recovering workflows, DBOS does not recover workflows belonging to different application versions. This prevents code compatibility issues.
• Workflows belonging to different app versions can be manually recovered with dbos workflow resume [workflow-ID].