Auto infer entries

[pi0]

Describe the feature

Currently entries should be explicitly specified as CLI args. We should add similar DX of unbuild to auto infer

Additional information

• Would you be willing to help implement this feature?

[Wyatex]

I also hope to implement this feature so that my unbuild project can be easily migrated to obuild

[pi0]

Feel free to draft a pull request if have time 👍🏼

[Wyatex]

I'll refer to unbuild and see if I can port this part of the code over.