Add policies for memorydb

[GomathiselviS]

Add policies for memorydb

The testcases in the PR fails because of permission issues. This PR adds the missing permissions to execute the memorydb testcases.

[alinabuzachis]

You should also add - 'arn:aws:iam::{{ aws_account_id }}:role/aws-service-role/memorydb.amazonaws.com/*' to https://github.com/mattclay/aws-terminator/blob/main/aws/policy/security-services.yaml#L177 and - 'memorydb.amazonaws.com'to https://github.com/mattclay/aws-terminator/blob/main/aws/policy/security-services.yaml#L188

All the classes, except that one that has create_time property, should subclass DbTerminator rather than Terminator.

[alinabuzachis]

I'm still testing, but you should also apply the changes we have suggested during the triage.

[alinabuzachis]

@GomathiselviS I added some new suggestions for some functions, but I would like to see @gravesm opinion's first.

[gravesm]

The better way to handle cases where some resource can't be deleted until another resource is deleted is to use age_limit. The AWS docs don't really describe the circumstances under which the various exceptions are raised. While SubnetUseInGroup seems pretty descriptive, InvalidUserStateFault sounds kind of generic.

[alinabuzachis]

Can be tested with this one ansible-collections/amazon.cloud#120 too.