Feat(auth): Rename authentication to auth (#6229)

**What**
- rename `authenticationModule` -> `authModule`

packages/auth/src/initialize/index.ts

@@ -0,0 +1,31 @@
+import {
+  ExternalModuleDeclaration,
+  InternalModuleDeclaration,
+  MODULE_PACKAGE_NAMES,
+  MedusaModule,
+  Modules,
+} from "@medusajs/modules-sdk"
+import { IAuthModuleService, ModulesSdkTypes } from "@medusajs/types"
+
+import { InitializeModuleInjectableDependencies } from "../types"
+import { moduleDefinition } from "../module-definition"
+
+export const initialize = async (
+  options?:
+    | ModulesSdkTypes.ModuleBootstrapDeclaration
+    | ModulesSdkTypes.ModuleServiceInitializeOptions
+    | ModulesSdkTypes.ModuleServiceInitializeCustomDataLayerOptions,
+  injectedDependencies?: InitializeModuleInjectableDependencies
+): Promise<IAuthModuleService> => {
+  const loaded = await MedusaModule.bootstrap<IAuthModuleService>({
+    moduleKey: Modules.AUTH,
+    defaultPath: MODULE_PACKAGE_NAMES[Modules.AUTH],
+    declaration: options as
+      | InternalModuleDeclaration
+      | ExternalModuleDeclaration, // TODO: Add provider configuration
+    injectedDependencies,
+    moduleExports: moduleDefinition,
+  })
+
+  return loaded[Modules.AUTH]
+}