update GuRole import in instance role

[jamie-lynch]

What does this change?

This PR updates the import of GuRole in the instance-role.ts file to import directly from the roles.ts file rather than the index.ts in the roles directory as this was causing an error when importing anything from @guardian/cdk/lib/constructs/iam.

Does this change require changes to existing projects or CDK CLI?

Any projects importing GuInstanceRole or GuRole from their specific file will now be able to get them from the @guardian/cdk/lib/constructs/iam path.

How to test

Bump to the latest version and try importing the GuInstanceRole construct from @guardian/cdk/lib/constructs/iam

How can we measure success?

All imports work as expected.

[jamie-lynch]

It looks like this issue didn't show up in our tests as the classes were only ever imported directly from their files. One thing that might be useful is to include some example stacks in this repository and try to build them during CI as an integration test.

As a side-effect, keeping these examples up to date alongside feature work might make it easier for users to see what a current "best practice" stack looks like and what changes are needed to incorporate new features. It would also give us a good test bed to trial features on as we work on them, rather than having to deploy and bump the version used in external projects.

I've started #209 to discuss this further.