[Feature Request] _select which step to do in `dpgen run`, and manually do some processes_

**Summary**

How about adding a "skip-stage" like parameter in dpgen run param parameters? When `dpgen run` deal with skipped stages, it just waits and checks the data needed by the next step prepared.

**Detailed Description**

I run dpgen script on a totally different machine from where I run FP calculations. I wonder whether I can do the FP calculation and collect the FP data manually, and just give the prepared result to dpgen again.
The fellow is what I do to get such processes:
- Give fake param and machine parameters about FP steps to let the dpgen shutdown at FP step (do stage 6 but not do stage 7)
- Manually collect the POSCAR prepared by dpgen.
- Run FP processes on another machine.
- Filter and collect FP output data.
- Add collected FP data to the system list and build a new folder to run a new `dpgen run` job.

I have to do such, because 1) I use FP software that dpgen does not support now, and 2) the machine I do FP can not automatically communicate with where I run dpgen script.

I wonder whether `dgen run` can add a param parameter to control which step to skip and wait for data manually prepared.