Alt text is not descriptive [.../hosting 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/guides/hosting/git-based-deployments.mdx:
```
44
45: 
46

48
49: 
50

52
53: 
54

56
57: 
58

60
61: 
62

64
65: 
66

68
69: 
```

 

https://github.com/aws-amplify/docs/blob/main/src/fragments/guides/hosting/nextjs.mdx:
```
131
132: 
133

183
184: 
185

272
273: 
274

276
277: 
278

284
285: 
286
```

 

https://github.com/aws-amplify/docs/blob/main/src/pages/[platform]/start/getting-started/hosting/index.mdx:
```
101
102: 
103

107
108: 
109
```