Enable index transformer

[vz-tl]

I noticed that the option for transforming index.html is already prepared but not finalized, however it apparently doesn't require a lot to make that work.

So I'd highly appreciate if this feature could be added to the plug-in soon!

For the meanwhile I temporarily added the functionality by monkey-patching the plugin package:

--- a/node_modules/@nx/angular-rspack/dist/lib/models/angular-rspack-plugin-options.d.ts
+++ b/node_modules/@nx/angular-rspack/dist/lib/models/angular-rspack-plugin-options.d.ts
@@ -138,12 +138,11 @@ export type IndexExpandedDefinition = {
     input: string;
     output?: string;
     preloadInitial?: boolean;
+    transformer?: IndexHtmlTransform;
 };
 export type IndexElement = IndexExpandedDefinition | string | false;
 export type IndexHtmlTransform = (content: string) => Promise<string>;
-export type NormalizedIndexElement = IndexExpandedDefinition & {
-    transformer: IndexHtmlTransform | undefined;
-};
+export type NormalizedIndexElement = IndexExpandedDefinition;
 export type NormalizedEntryPoint = Required<Exclude<ScriptOrStyleEntry, string>>;
 export interface SourceMap {
     scripts: boolean;

--- a/node_modules/@nx/angular-rspack/dist/lib/models/normalize-options.js
+++ b/node_modules/@nx/angular-rspack/dist/lib/models/normalize-options.js
@@ -126,8 +126,7 @@ async function normalizeOptions(options) {
     const index = {
         input: (0, node_path_1.resolve)(root, typeof options.index === 'string' ? options.index : options.index.input),
         output: indexOutput,
-        // @TODO: Add support for transformer
-        transformer: undefined,
+        transformer: typeof options.index === 'object' ? options.index.transformer : undefined,
         // Preload initial defaults to true
         preloadInitial: typeof options.index !== 'object' ||
             (options.index.preloadInitial ?? true),

--- a/node_modules/@nx/angular-rspack/dist/lib/plugins/ng-rspack.js
+++ b/node_modules/@nx/angular-rspack/dist/lib/plugins/ng-rspack.js
@@ -97,6 +97,7 @@ class NgRspackPlugin {
                 entrypoints: (0, entry_points_1.getEntryPoints)(this.pluginOptions.globalStyles, this.pluginOptions.globalScripts, this.pluginOptions.devServer?.hmr),
                 i18n: this.i18n,
                 optimization: this.pluginOptions.optimization,
+                postTransform: this.pluginOptions.index.transformer,
                 isSsr: !!(this.pluginOptions.ssr ||
                     this.pluginOptions.prerender ||
                     this.pluginOptions.appShell),

[Coly010]

Feel free to open a PR :)