feat: support config file as typescript

[AriPerkkio]

Add support for AriPerkkio/eslint-remote-tester#318.

Configuration file name is read from Action arguments:

eslint-remote-tester-run-action/src/index.ts

Lines 17 to 20 in 223700c

	const eslintRemoteTesterConfig = core.getInput(
	'eslint-remote-tester-config',
	{ required: true }
	);

User's configuration file is extended by internal configuration:

eslint-remote-tester-run-action/src/run-tester.ts

Lines 68 to 72 in 223700c

	// Write eslint-remote-tester configuration file
	fs.writeFileSync(
	INTERNAL_CONFIG,
	CONFIGURATION_TEMPLATE(usersConfigLocation)
	);

We might want to have CONFIGURATION_TEMPLATEs for Javascript and Typescript separately:

eslint-remote-tester-run-action/src/run-tester.ts

Lines 23 to 33 in 223700c

	const CONFIGURATION_TEMPLATE = (
	pathToUsersConfiguration: string
	) =>
	`// Generated by eslint-remote-tester-run-action
	const fs = require('fs');
	// Load user's eslint-remote-tester.config.js
	const usersConfig = require('${pathToUsersConfiguration}');
	module.exports = {
	...usersConfig,

    // Write eslint-remote-tester configuration file
    fs.writeFileSync(
        INTERNAL_CONFIG,
-       CONFIGURATION_TEMPLATE(usersConfigLocation)
+       usersConfigLocation.endsWith('.js') ? 
+           CONFIGURATION_TEMPLATE_JS(usersConfigLocation) :
+           CONFIGURATION_TEMPLATE_TS(usersConfigLocation)
    );