Warn when multiple configs are found

[SimenB]

🚀 Feature Proposal

From #10123.

When we find a config file, we should also check if there is a jest entry in any sibling package.json and print a warning that it is ignored.

If using --config we should not warn.

Motivation

Helps the user have correct and consistent configuration and helps when trying to debug why config is not applied.

Example

$ jest
● Multiple configurations found:

  Jest will use `path/to/jest.config.js` for configuration, but Jest also
  found configuration in `path/to/package.json`. Delete the `"jest"` key
  in that file to silence this warning, or delete the `jest.config.js` file
  to use the configuration from `package.json`.

  Configuration Documentation:
  https://jestjs.io/docs/en/configuration.html

[Mansehej]

Hey,
Mind if I give it a try as my first issue?

[thymikee]

@Mansehej go for it!

[AndresContreras96]

Hello @Mansehej are you keep working on this issue?

[Mansehej]

Hey @AndresContreras96, I am indeed. I have, infact, got it working, I'm trying to figure out writing tests for it.

[mgm793]

Hey, I create a PR to solve it! #10798

[Adomyanmarcitizen]

How to do at I really don't understand.

[hallelshohat]

can I Work on it?

[jankaifer]

I'm working on it.

[SimenB]

https://github.com/facebook/jest/releases/tag/v27.2.5

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