Alt text is not descriptive [.../graphqlapi files]

**Describe the content issue**:
Images listed below do not have descriptive/informative alt text. For markdown the alt text is located between the square brackets, ``.

The list below isn't exhaustive since I found these images based on the word count for the alt text, but it should be a good starting point to make our alt text better for people who use screen readers.

Some resources to help write alt text:
- https://webaim.org/techniques/alttext/
- https://www.a11yproject.com/posts/are-you-making-these-five-mistakes-when-writing-alt-text/

https://github.com/aws-amplify/docs/blob/main/src/fragments/sdk/api/ios/graphql.mdx:
```
258
259: 
260
```

https://github.com/aws-amplify/docs/blob/main/src/pages/[platform]/build-a-backend/graphqlapi/connect-api-to-existing-database/index.mdx:
```
83
84: 
85
```

Start with src/fragments/sdk/api/ios/graphql.mdx and src/pages/[platform]/build-a-backend/graphqlapi/connect-api-to-existing-database/index.mdx, then review the linked WebAIM and A11y Project guidance. Replace the listed non-descriptive image alt text with informative descriptions, and check that both referenced images have alt text that conveys their content to screen-reader users.

Written by the indexing model from the issue text.