flow config add deployment incorrectly includes previewnet as an option

[chasefleming]

Description:
The flow config add deployment command currently lists previewnet as one of the selectable networks. Since previewnet is deprecated, it should no longer appear as an option in the deployment configuration process. This option should be removed to prevent confusion and ensure only valid networks are presented to users.

[diego-noah]

hey @chasefleming can i work on this

[diego-noah]

@chasefleming Should we only remove previewnet from the interactive prompt in flow config add deployment, or should it be removed from all CLI commands/configurations? This would help clarify if we need to make changes in other places beyond the prompt UI. When users try to use previewnet through command flags (e.g., flow config add deployment --network previewnet), should we return an error message indicating it's deprecated? If yes, what message would you prefer to show to users?