framework-integ: Support specification of awsPcaAuthorityArn in framework integ tests

[ren-yamanashi]

Describe the issue

Currently, the following document on integ testing of the framework does not describe the specification of awsPcaAuthorityArn.

https://github.com/aws/aws-cdk/blob/main/packages/%40aws-cdk-testing/framework-integ/README.md

However, in the following MR that I am currently working on, I encountered a use case where I want to specify awsPcaAuthorityArn in the integ test.

#32605

Therefore, I would like you to add support for specifying awsPcaAuthorityArn in integ tests.
(I expect it will probably be in the form of adding an environment variable).

Thank you in advance.

Links

https://github.com/aws/aws-cdk/blob/main/packages/%40aws-cdk-testing/framework-integ/README.md