Alt text is not descriptive [push-notification pages]

**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/lib/push-notifications/android/setup_push_service/setup-fcm.mdx:
```
14
15: 
16

19
20: 
21

25
26: 
27
```

 

https://github.com/aws-amplify/docs/blob/main/src/fragments/lib/push-notifications/common/enable-rich-notifications.mdx:
```
43
44: 
45

47
48: 
```

 

https://github.com/aws-amplify/docs/blob/main/src/fragments/lib/push-notifications/ios/getting_started/20_set_entitlements.mdx:
```
22
23: 
24

32
33: 
34

36
37: 
38

40
41: 
42
```

 

https://github.com/aws-amplify/docs/blob/main/src/fragments/lib/push-notifications/ios/remote_media/10_remote_media.mdx:
```
12
13: 
14

16
17: 
18

20
21: 
22

24
25: 
26

28
29: 
30
```

 

https://github.com/aws-amplify/docs/blob/main/src/fragments/lib/push-notifications/ios/setup_push_service/setup-apns.mdx:
```
35
36: 
37

39
40: 
41

43
44: 
45

48
49: 
50

52
53: 
54

69
70: 
71

73
74: 
75

77
78: 
79

81
82: 
83

88
89: 
90

92
93: 
94
```

 

https://github.com/aws-amplify/docs/blob/main/src/fragments/lib-v1/push-notifications/react-native/enable_rich_notifications/enable-rich-notifications.mdx:
```
37
38: 
39

41
42: 
```