[Feature]: use cpu limit for maxWorker, not cpu cores length

[Diokuz]

🚀 Feature Proposal

There is a problem with jest in docker with cpu limits nodejs/node#28762

Motivation

nodejs/node#28762 ← this problem leads to very long (or even never) task completion.

Example

There are three options could be done:

1. Use cpu limit (e.g. https://github.com/xiaoxiaojx/get_cpus_length) to setup the default value of maxWorkers
2. Use --runInBand by default when process.env.CI is defined
3. Make it possible to change maxWorkers via env, e.g.

JEST_MAX_WORKERS=3 npx jest

Pitch

Because you provide the default value of https://jestjs.io/docs/cli#--maxworkersnumstring

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This issue was closed because it has been stalled for 7 days with no activity. Please open a new issue if the issue is still relevant, linking to this one.

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