feat(config): add .cjs file extension config support

docs/development/configuration.md

@@ -24,6 +24,8 @@ If you need an alternate location or name, set it in the environment variable `R
 For example `RENOVATE_CONFIG_FILE=myconfig.js` or `RENOVATE_CONFIG_FILE=myconfig.json` and not `RENOVATE_CONFIG_FILE=myconfig`.
 If none is provided, or the file type is invalid, Renovate will fail.
 
+If you are in an ESM repo (`"type": "module"` in `package.json`) then you must use a `.cjs` extension and set `RENOVATE_CONFIG_FILE`. For example `RENOVATE_CONFIG_FILE=myconfig.cjs`.
+
 Using a configuration file gives you very granular configuration options.
 For instance, you can override most settings at the global (file), repository, or package level.
 e.g. apply one set of labels for `backend/package.json` and a different set of labels for `frontend/package.json` in the same repository.

lib/workers/global/config/parse/__fixtures__/config.cjs

@@ -0,0 +1,3 @@
+module.exports = {
+  token: 'abcdefg',
+};

lib/workers/global/config/parse/file.spec.ts

@@ -24,6 +24,7 @@ describe('workers/global/config/parse/file', () => {
   describe('.getConfig()', () => {
     it.each([
       ['custom js config file', 'config.js'],
+      ['custom js config file', 'config.cjs'],
       ['custom js config file exporting a Promise', 'config-promise.js'],
       ['custom js config file exporting a function', 'config-function.js'],
       // The next two are different syntactic ways of expressing the same thing

lib/workers/global/config/parse/file.ts

@@ -25,6 +25,7 @@ export async function getParsedContent(file: string): Promise<RenovateConfig> {
         await readSystemFile(file, 'utf8'),
         file,
       ) as RenovateConfig;
+    case '.cjs':
     case '.js': {
       const tmpConfig = await import(file);
       let config = tmpConfig.default