fix(IAM Identity): add PowerVS compute resource type support

[briangleeson]

PR summary

This PR replaces and fixes this previous PR: #324

• Add support for PowerVS compute resource type
• Fix issue with value_string in Identity Preference handling by making it not required

PR Checklist

Please make sure that your PR fulfills the following requirements:

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

Does this PR introduce a breaking change?

• Yes
• No

Other information

$ make test-int
python -m pytest test/integration/test_iam_identity_v1*
=================== test session starts ===================
platform win32 -- Python 3.14.4, pytest-7.4.4, pluggy-1.6.0
rootdir: C:\Snaps\terraform\platform-services-python-sdk
collected 105 items
============= 105 passed in 798.26s (0:13:18) =============


$ make test-examples
python -m pytest examples/test_iam_identity_v1*
=================== test session starts ===================
platform win32 -- Python 3.14.4, pytest-7.4.4, pluggy-1.6.0
rootdir: C:\Snaps\terraform\platform-services-python-sdk
collected 83 items

examples\test_iam_identity_v1_examples.py .......    [100%]

============== 83 passed in 746.63s (0:12:26) =============

[CLAassistant]

All committers have signed the CLA.

[pyrooka]

Looks good!

[ibm-devx-sdk]

🎉 This PR is included in version 0.75.1 🎉

The release is available on GitHub release

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