Use flag for CAPI Image Builder to clear ephemeral keys

[brinker211]

Is your feature request related to a problem? Please describe.

As a user using Azure Defender there is an alert for keys present on the control plane nodes in CAPZ.

Describe the solution you'd like

Test or try a flag such as ssh_clear_authorized_keys to clear the ephemeral keys for CAPI image builder.

Describe alternatives you've considered

Additional context

This is low priority.

[ericgraf]

All new images built will have this setting enabled.
All previously generated images do not have this but they can be requested if really required.