Include a marker file to signal bundle download and extraction was successfully completed

Currently, the host has no reliable way to verify whether a downloaded bundle was fully and successfully retrieved. If the host encounters an error during the download or extraction process, it may result in a partially downloaded bundle. If a newer host version later attempts to load this incomplete bundle, it can cause hard-to-diagnose issues in the function app.
This issue is most commonly observed in Core Tools, where developers download bundles locally during development.

### Proposed Solution
Introduce a completion marker file that the host can check to confirm the bundle was fully downloaded and extracted. The presence of this file would indicate a successful operation, while its absence would signal an incomplete or failed download.