tests: mock API calls in +page.ts file

[MRita443]

Our current integration with MSW seems to function only when the API calls are done within the <script> tag of the +page.svelte file. From our experiments, which included attempting to mock the +page.js module, researching specific support from the msw-storybook-addon package, and switching the loading code to +page.svelte, we could not get this to work with the loading code in +page.ts. The problem with having the code in the svelte page is that errors thrown are not presented with the +error.svelte page.