NewHandler should be cleaned up

[jakedoublev]

Background

The cmd package has a helper function NewHandler that does a lot of setup work for every command: https://github.com/opentdf/otdfctl/blob/main/cmd/root.go#L72

There is quite a bit of complexity in nested if statements, and it should be explored if it can be a preRun hook

Acceptance Criteria

1. nested if complexity is reduced
2. exploration about a preRun hook on every command that needs a handler available to it
3. unit tests as appropriate