feat(core): make it possible to use environment variable to set cache…

… directory

Use the environment variable NX_CACHE_DIRECTORY to set the cache directory.
This would override the cache directory set in nx.json.

ISSUES CLOSED: #6629

packages/workspace/src/utilities/cache-directory.ts

@@ -2,6 +2,10 @@ import { join } from 'path';
 import { readJsonFile } from './fileutils';
 
 export function readCacheDirectoryProperty(root: string) {
+  const cacheDir = process.env.NX_CACHE_DIRECTORY;
+  if (cacheDir) {
+    return cacheDir;
+  }
   try {
     const nxJson = readJsonFile(join(root, 'nx.json'));
     return nxJson.tasksRunnerOptions.default.options.cacheDirectory;