Refactor everything to ES Modules

[FloEdelmann]

These are the changes from #1626 again, which has been reverted in #1926.

Since #1930 is now merged, we shouldn't have to wait for Unitech/pm2#4540 to be fixed.

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ECMAScript Modules (ESM) support first appeared without a command-line flag in Node.js v14: https://nodejs.org/docs/latest-v14.x/api/esm.html

In Node, import does not work with .json files (without another command-line flag), that's why in #1623 I replaced them and in #1625 implemented a workaround.

To do after this is merged

• Drop esm dependency from package.json
• Enable import/no-duplicates rule
• Enable import/order rule
• Enable import/newline-after-import rule
• Enable import/first rule
• Enable import/exports-last rule
• Replace unicorn/import-style configuration with no-restricted-imports
• Remove explicit disabling of unicorn/prefer-node-protocol rule once Support node: protocol unjs/jiti#30 is fixed