SCP for denying creation of unencrypted Neptune DB

[bksarthak]

Use Case - Is your feature request related to a problem? Please describe.
Neptune DB is a graph DB service by AWS. An SCP is needed to prevent creation of unecrypted Neptune DB

Expected Outcome - Describe the solution you'd like
Ability for customer to prevent creation of unencrypted graph databases using Neptune

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Affected AWS resource
Amazon Neptune

Impact
High: The issue makes a service level improvement which affects all users of AWS
Medium: Single feature which affects a single functionality which is optionally enabled in the AWS service
Low: Niche use case which is particularly affecting the AWS resources if it is configured in a certain way
Medium

Supported material
Can be either logs, screenshots or documentation links which provide evidence of need of this issue

**I can contribute: Yes

Additional context
Add any other context or screenshots about the feature request here.

Pull Request number
#15

[bksarthak]

ready to merge