Yarn config respect --no-defaults with --json (fixes yarnpkg#6341)

As documented here https://yarnpkg.com/cli/config you would expect `--no-defaults` to omit defaults even when `--json` is also specified.

This commit fixes that behaviour to be as expected.

Author: sparrowt

packages/plugin-essentials/sources/commands/config.ts

@@ -76,6 +76,9 @@ export default class ConfigCommand extends BaseCommand {
 
       if (this.json) {
         for (const name of names) {
+          if (this.noDefaults && !configuration.sources.has(name))
+            continue;
+
           const data = configuration.settings.get(name);
           if (typeof data === `undefined`)
             report.reportError(MessageName.INVALID_CONFIGURATION_KEY, `No configuration key named "${name}"`);