Support configurable location for `main.go` via `--main-file` flag

[afritzler]

What do you want to happen?

Currently, kubebuilder scaffolding expects the manager’s main.go to be located at the root of the cmd directory (cmd/main.go). This assumption limits flexibility when structuring projects according to standard Go project layouts.

For example, if I want to add additional commands (e.g., CLI tooling), I would like to place them in their own subdirectories under cmd/, such as:

cmd/
  manager/
    main.go
  foocli/
    main.go

To support this structure, I propose adding a --main-file flag (e.g., --main-file=cmd/manager/main.go) to allow the main manager entry point to be specified explicitly during scaffolding or plugin operations.

Additionally, this path could be recorded in the PROJECT config file to persist the custom layout and support tooling/codegen accordingly.

Would the maintainers be open to a PR adding this feature?

Extra Labels

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