Add more logging when the function app goes into offline mode

Currently when the function app goes into offline mode we have minimal logs which basically says `Host is offline.` We need to add more logging to basically show what action or when we initiated the process of bringing the app offline.

Start by locating the existing `Host is offline.` log and trace the function app's transition into offline mode. Done means the host logs which action initiated the transition and when the process began, providing more context than the current message.

Written by the indexing model from the issue text.