DEV: Reduce Webpack memory use in development (#24387)

The default for webpack is to keep cached values indefinitely. In discourse, this unbound memory usage causes node to raise an OOM error after 50-100 rebuilds in development mode (with source maps enabled). Setting maxGenerations=1 means that the cache will be cleaned up regularly. With this change, I see no discernible increase in memory after 150+ rebuilds.

app/assets/javascripts/discourse/ember-cli-build.js

@@ -139,6 +139,12 @@ module.exports = function (defaults) {
         output: {
           publicPath: "auto",
         },
+        cache: isProduction
+          ? false
+          : {
+              type: "memory",
+              maxGenerations: 1,
+            },
         entry: {
           "assets/discourse.js/features/markdown-it.js": {
             import: "./static/markdown-it",