Vite embedded build of Element Call (#3077)

* Embedded package build of Element Call

Part of https://github.com/element-hq/element-call/issues/2994

This creates a new "embedded" build (vs "full" build) at the vite level. It will be used by a later PR that actually provides platform specific packages.

Embedded build:

- Uses relative URLs
- Uses relative config.json path and other resource loading
- Has a config.json built in
- Doesn't include the public folder (e.g. favicon)

Out of scope:

- this doesn't attempt to exclude SPA functionality, so technically the build could be used in SPA
- the above means that the crypto-wasm binary is included in the build

* CI artifact name based on type of build

* Update src/config/Config.ts

vite-embedded.config.js

@@ -0,0 +1,31 @@
+import { defineConfig, mergeConfig } from "vite";
+import fullConfig from "./vite.config";
+import generateFile from "vite-plugin-generate-file";
+
+const base = "./";
+
+// Config for embedded deployments (possibly hosted under a non-root path)
+export default defineConfig((env) =>
+  mergeConfig(
+    fullConfig({ ...env, packageType: "embedded" }),
+    defineConfig({
+      base, // Use relative URLs to allow the app to be hosted under any path
+      publicDir: false, // Don't serve the public directory which only contains the favicon
+      plugins: [
+        generateFile([
+          {
+            type: "json",
+            output: "./config.json",
+            data: {
+              matrix_rtc_session: {
+                key_rotation_on_leave_delay: 15000,
+                membership_keep_alive_period: 5000,
+                membership_server_side_expiry_timeout: 15000,
+              },
+            },
+          },
+        ]),
+      ],
+    }),
+  ),
+);