add non-global resource example for function's `custom-policies.json`

**Is your feature request related to a problem? Please describe.**

Currently examples for `custom-policies.json` use global resources as an example, whereas other resources such as SSM will require wildcards (`*`) in place of the placeholder `:::` in the resource ARN

https://docs.amplify.aws/cli/function/#access-existing-aws-resource-from-lambda-function

example policy for accessing parameters

```json
[
{
"Action": ["ssm:GetParameters"],
"Resource": [
"arn:aws:ssm:*:*:parameter/*"
]
}
]

```

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