MSW: Add mock definition for /provisioning/v1/sources end point

This commit adds the necessarily handler, resolver, and server to use
MSW for mocking the /provisioning/v1/sources endpoint.

The server can be used in tests like so:
```javascript
// src/setupTests.js
import { server } from './mocks/server.js'
// Establish API mocking before all tests.
beforeAll(() => server.listen())

// Reset any request handlers that we may add during the tests,
// so they don't affect other tests.
afterEach(() => server.resetHandlers())

// Clean up after the tests are finished.
afterAll(() => server.close())
```

src/constants.js

@@ -1,6 +1,7 @@
 export const IMAGE_BUILDER_API = '/api/image-builder/v1';
 export const RHSM_API = '/api/rhsm/v2';
 export const CONTENT_SOURCES = '/api/content-sources/v1';
+export const PROVISIONING_SOURCES_ENDPOINT = '/api/provisioning/v1/sources';
 export const RHEL_8 = 'rhel-87';
 export const RHEL_9 = 'rhel-91';
 

src/store/apiSlice.js

@@ -1,11 +1,13 @@
 import { createApi, fetchBaseQuery } from '@reduxjs/toolkit/query/react';
 
+import { PROVISIONING_SOURCES_ENDPOINT } from '../constants';
+
 export const apiSlice = createApi({
   reducerPath: 'api',
-  baseQuery: fetchBaseQuery({ baseUrl: '/api' }),
+  baseQuery: fetchBaseQuery({ baseUrl: '' }),
   endpoints: (builder) => ({
     getSources: builder.query({
-      query: () => '/provisioning/v1/sources',
+      query: () => PROVISIONING_SOURCES_ENDPOINT,
     }),
   }),
 });

src/test/mocks/handlers.js

@@ -0,0 +1,21 @@
+import { rest } from 'msw';
+
+import { PROVISIONING_SOURCES_ENDPOINT } from '../../constants';
+
+const baseURL = 'http://localhost';
+
+export const handlers = [
+  rest.get(baseURL.concat(PROVISIONING_SOURCES_ENDPOINT), (req, res, ctx) => {
+    return res(
+      ctx.status(200),
+      ctx.json([
+        {
+          id: '123',
+          name: 'my_source',
+          source_type_id: '1',
+          uid: 'de5e35d4-4c1f-49d7-9ef3-7d08e6b9c76a',
+        },
+      ])
+    );
+  }),
+];

src/test/mocks/server.js

@@ -0,0 +1,5 @@
+import { setupServer } from 'msw/node';
+
+import { handlers } from './handlers';
+
+export const server = setupServer(...handlers);