feat(iam-identity): Add PowerVS compute resource type support

[briangleeson]

PR summary

This PR replaces and fixes this previous PR: IBM/platform-services-java-sdk#302

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

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

$ npm run test-unit
Test Suites: 22 passed, 22 total
Tests:       1859 passed, 1859 total
Snapshots:   0 total
Time:        7.888 s, estimated 17 s
Ran all test suites matching /test\\unit\\/i.

Test Suites: 1 passed, 1 total
Tests:       78 passed, 78 total
Snapshots:   0 total
Time:        785.121 s
Ran all test suites matching /test\\integration\\iam-identity*/i.

[CLAassistant]

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