AWS::Cloud9::EnvironmentEC2 NewAttribute-UserData

**1. Title**
AWS::AWS::Cloud9::EnvironmentEC2-NewAttribute-UserData

**2. Scope of request**
ability to run custom scripts in cloud9 when creating it

**3. Expected behavior**
Ideally configure cloud9 to clone git repos from a central enterprise codecommit account. We acheive this by running a script that sets git creds. If it can be automated at creation, that would be great as it can be integrated with service catalogs.

Hence, developers can create a cloud9 environment without having to worry about git configurations. It would really be a one-click deployment

**4. Suggest specific test cases**
it should help me create an ACM Certificate given that the same account is the authority for the domain name used in the certificate.

**5. Helpful Links to speed up research and evaluation.**

Something similar to userdata field of an EC2 instance.

Updated API docs at https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-properties-ec2-instance.html

**6. Category (required) - Compute (EC2, ECS, EKS, Lambda)**

Start with the AWS::Cloud9::EnvironmentEC2 resource and the linked CloudFormation EC2 UserData documentation. Clarify how creation-time scripts should be configured and how the CodeCommit and ACM scenarios define success; the issue does not mention repository files or tests.

Written by the indexing model from the issue text.