fix(NA): missing --openssl-legacy-provider on webpack worker inside p…

…lugin helpers (#169030)

This PR fixes a problem inside plugin-helpers as the webpack runner was
running without `--openssl-legacy-provider` which breaks in the latest
node version.

packages/kbn-plugin-helpers/src/tasks/optimize.ts

@@ -63,7 +63,7 @@ export async function optimize({
 
     const proc = fork(require.resolve('./optimize_worker'), {
       cwd: REPO_ROOT,
-      execArgv: ['--require=@kbn/babel-register/install'],
+      execArgv: ['--require=@kbn/babel-register/install', '--openssl-legacy-provider'],
       stdio: ['ignore', 'pipe', 'pipe', 'ipc'],
     });