refactor: add missing mts ext. support to checkly config

[kiroushi]

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Affected Components

• CLI
• Create CLI
• Test
• Docs
• Examples
• Other

Notes for the Reviewer

Currently the CLI is able to read both JS/TS files, or .mjs when the app is declared as commonjs and needs to be interpreted as a ESM; but is missing the ability to do so when the config is written in TypeScript.

This PR adds the .mts extension to the list of candidates to read the config from to allow certain settings like https://www.typescriptlang.org/tsconfig/#verbatimModuleSyntax to work while in commonjs apps.

[sorccu]

Are you sure that the current changes are enough? I don't think this works without changing loadFile too:

checkly-cli/packages/cli/src/services/checkly-config-loader.ts

Lines 77 to 97 in 9072477

	enum Extension {
	JS = '.js',
	MJS = '.mjs',
	TS = '.ts',
	}
	export function loadFile (file: string) {
	if (!existsSync(file)) {
	return Promise.resolve(null)
	}
	switch (path.extname(file)) {
	case Extension.JS:
	return loadJsFile(file)
	case Extension.MJS:
	return loadJsFile(file)
	case Extension.TS:
	return loadTsFile(file)
	default:
	throw new Error(`Unsupported file extension ${file} for the config file`)
	}
	}

Without adding mts there, you'll just get an error saying checkly.config.mts is unsupported which makes no sense.

Additionally loadTsFile may potentially need some changes for modules (perhaps similar to loadJsFile), not completely sure about that without trying it out.

Either way I wouldn't really call this a refactor. I would like you to change this to feat instead because that's what it is, and it should therefore come with at least 1 test to prove that it works, or at minimum you must provide some proof that it worked for you locally.

[sorccu]

See my comment

[sorccu]

Also I would like to know the motivation for this change. I agree that it's good but just wondering what made you think of doing it.