feat(config): add defineConfig and mergeConfig functions

[ahnpnl]

Summary

Inspired from Vite and Playwright, this PR introduces 2 new functions to jest-config: defineConfig and mergeConfig.

This will greatly improve DX that developers:

• Don't need to know which interface to use
• Get autocomplete OOTB
• Don't need to use JSDOC comment for types

Test plan

• Added unit tests and e2e tests
• Green CI

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commit: 565fc14

[ahnpnl]

Hi @cpojer @SimenB would you pls help me to check this PR? Thank you 🙏