fix(IAM Policy Management): update subject attribute value

[swcolley]

Issue: https://github.ibm.com/IAM/AM-issues/issues/2140

PR summary

Minor fix of subject attribute value type to match API and other attributes value type.

PR Checklist

Please make sure that your PR fulfills the following requirements:

• [x] The commit message follows the Angular Commit Message Guidelines.
• [x] Tests for the changes have been added (for bug fixes / features)
• [x] Docs have been added / updated (for bug fixes / features)

Current vs new behavior

Subject attribute value should not be limited to a string, but should allow for other types based on API. This change allows that.

Does this PR introduce a breaking change?

• [ ] Yes
• [x] No

Other information

Out of testing: Integration tests:

shaunsmacibm@Shauns-MacBook-Pro iampolicymanagementv1 % go test -tags=integration
Running Suite: IamPolicyManagementV1 Suite
==========================================
Random Seed: 1705526859
Will run 212 of 212 specs

••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••
Ran 212 of 212 Specs in 19.390 seconds
SUCCESS! -- 212 Passed | 0 Failed | 0 Pending | 0 Skipped
PASS

examples:

Ran 214 of 214 Specs in 28.957 seconds
SUCCESS! -- 214 Passed | 0 Failed | 0 Pending | 0 Skipped
--- PASS: TestIamPolicyManagementV1 (29.02s)
PASS

[ibm-devx-sdk]

:tada: This PR is included in version 0.56.3 :tada:

The release is available on GitHub release

Your semantic-release bot :package::rocket: