Python Flask apps require Flask debug = False to be set

[etanshaul]

Without this, it seems, that Cloud Code debugging doesn't work.

Done when -

1. We either document this limitation, or
2. We update the logic to avoid this limitation.

Two threads with evidence of this:

1. https://github.com/GoogleCloudPlatform/cloud-code-intellij/issues/3059#issuecomment-1057548056
2. https://github.com/GoogleCloudPlatform/cloud-code-intellij/issues/2961