chocolatey-agent upgrade documentation could make it clearer what you see when upgrading with chocolatey-agent

## Is Your Feature Request Related To A Problem? Please describe.

The [current documentation](https://docs.chocolatey.org/en-us/agent/upgrade) lists the ways to upgrade. This includes using a CCM Deployment and a possible scheduled task to restart the `chocolatey-agent` service to change to the new version. It should be more clear about what types of output you'll see in the logs if the upgrade is done through `chocolatey-agent` (There are errors about trying to remove the `exe` because it's in use by the service).

## Describe The Solution. Why is it needed?

Document some of the errors that may be expected in either terminal output or log files.

## Additional Context.

The upgrade of the agent is successful, but the executable can't be removed as the service is still running. This only happens when the agent is the one performing the upgrade (through CCM deployment, or background agent configuration in C4B).

## Related Issues

[Zendesk ticket](https://chocolatey.zendesk.com/agent/tickets/13180)