Support charm upgrades by dropping a .zip on the inspector

To QA
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- Deploy a real environment.
- Drag and drop a local charm .zip from your desktop to the canvas and deploy.
- After it turns green open it's inspector.
- Drag and drop the same charm on the inspector
- You should get a notification that it completed successfully.
- If you wait a few seconds you will then get a notification in the inspector that the service has been upgraded.

__Notes__
You will need at least Juju 1.17.2
A small and quick to deploy charm: https://github.com/hatched/ghost-charm
If you are using Juju 1.17.2 and download the zip form Github you will need to repack it so that the files sit at the root of the zip. Juju 1.17.3 does not have this restriction.