Add FilterPolicyScope SNS property

[torrescd]

Description of your changes

Add FilterPolicyScope SNS property

I have:

• Read and followed Crossplane's [contribution process].
• Run make reviewable test to ensure this PR is ready for review.

How has this code been tested

Tested on custom image devopsmindset/provider-aws:v0.0.0-2805.gc24807d8 with proper sns

[chlunde]

Thanks, tested OK:

apiVersion: sns.aws.crossplane.io/v1beta1
kind: Subscription
metadata:
  name: sample-subscription
spec:
  forProvider:
    region: us-east-1
    protocol: email
    filterPolicyScope: MessageBody
    filterPolicy: |
       {
         "foo": ["bar"]
       }
    endpoint: crossplane-test@mailinator.com
    topicArnRef:
      name: some-topic
  providerConfigRef:
    name: example