Vitest (#6219)

Port to vitest. Port everything to typescript. Remove chai, mocha and
chai-as-promised. Adds some docs.

vitest.config.ts

@@ -0,0 +1,11 @@
+// eslint-disable-next-line node/no-unpublished-import
+import {defineConfig} from 'vitest/config';
+
+// eslint-disable-next-line import/no-default-export
+export default defineConfig({
+    test: {
+        include: ['test/**/*.ts'],
+        exclude: ['test/_*.ts', 'test/utils.ts'],
+        setupFiles: ['/test/_setup-fake-aws.ts', '/test/_setup-log.ts'],
+    },
+});