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

### 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.

https://github.com/aws/aws-cdk/pull/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

Start with packages/@aws-cdk-testing/framework-integ/README.md and inspect the use case in pull request #32605. Trace how framework integ tests receive configuration, then add support for specifying awsPcaAuthorityArn and document it in the README; done means the setting is accepted by integ tests and its usage is described.

Written by the indexing model from the issue text.