Feature: possibility to have more than one SCP in adf-bootstrap

Hi,

when bootstrapping accounts via ADF it's possible to use "only" one Service Control Policy (in the form of scp.json file within the adf-bootstrap folder from the aws-deployment-framework-bootstrap repository on the Master Account).

When such scp.json exceed the maximum allowed limit of 5KB, it cause an issue:
`An error occurred (ConstraintViolationException) when calling the UpdatePolicy operation: You have exceeded the maximum policy size`

It would be good to have adf managing more than one SCPs, like for example in a folder like this:
scp
|__ scp1.json
|__ scp2.json
|__ ...

Start with scp.json in the adf-bootstrap folder of the aws-deployment-framework-bootstrap repository and trace how the bootstrap process discovers and submits its policy. The issue is complete when adf-bootstrap can manage multiple SCP files so an individual policy stays within AWS's 5KB limit.

Written by the indexing model from the issue text.