improve validation on `sign in with apple` private key

### How did you install the Amplify CLI?

_No response_

### If applicable, what version of Node.js are you using?

_No response_

### Amplify CLI Version

12.2.3

### What operating system are you using?

mac

### Did you make any manual changes to the cloud resources managed by Amplify? Please describe the changes made.

no

### Describe the bug

It appears the validation on CLI allows just typing in the begin and end of the private key

### Expected behavior

validate and throw appropriate message

### Reproduction steps

1. add auth
2. select `signin with apple`
3. enter the begin and end without the hash key
4. observe no errors

### Project Identifier

_No response_

### Log output

```
# Put your logs below this line

```

### Additional information

_No response_

### Before submitting, please confirm:

- [X] I have done my best to include a minimal, self-contained set of instructions for consistently reproducing the issue.
- [X] I have removed any sensitive information from my code snippets and submission.