fix(IAM Policy Management): Update check for authorization policy subject and add test coverage

[swcolley]

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Relates OR Closes #2212

This adds test cases to make sure stringMatch is valid as well as fixes an input check for authorization policy.

Output from acceptance testing:

All of the authorization tests:

$ go test ./ibm/service/iampolicy/ -run=TestAccIBMIAMAuthorizationPolicy_ -timeout 700m -v
...
PASS
ok  	github.com/IBM-Cloud/terraform-provider-ibm/ibm/service/iampolicy	357.904s
```

Tests added for each policy type
Access group test:
```sh
$ go test ./ibm/service/iampolicy/ -run=TestAccIBMIAMAccessGroupPolicy_StringMatch_Without_Wildcard -timeout 700m -v
...
=== RUN   TestAccIBMIAMAccessGroupPolicy_StringMatch_Without_Wildcard
--- PASS: TestAccIBMIAMAccessGroupPolicy_StringMatch_Without_Wildcard (23.43s)
PASS
ok  	github.com/IBM-Cloud/terraform-provider-ibm/ibm/service/iampolicy	26.051s

service policy test:

$ go test ./ibm/service/iampolicy/ -run=TestAccIBMIAMServicePolicy_With_Resource_Attributes_Without_Wildcard -timeout 700m -v
=== RUN   TestAccIBMIAMServicePolicy_With_Resource_Attributes_Without_Wildcard
--- PASS: TestAccIBMIAMServicePolicy_With_Resource_Attributes_Without_Wildcard (23.87s)
PASS
ok  	github.com/IBM-Cloud/terraform-provider-ibm/ibm/service/iampolicy	25.931s

trusted profile test

=== RUN   TestAccIBMIAMTrustedProfilePolicy_With_Resource_Attributes_Without_Wildcard
--- PASS: TestAccIBMIAMTrustedProfilePolicy_With_Resource_Attributes_Without_Wildcard (28.18s)
PASS
ok  	github.com/IBM-Cloud/terraform-provider-ibm/ibm/service/iampolicy	30.317s

user policy test

--- PASS: TestAccIBMIAMUserPolicy_With_Resource_Attributes_Without_Wildcard (33.04s)
PASS
ok  	github.com/IBM-Cloud/terraform-provider-ibm/ibm/service/iampolicy	35.134s

[swcolley]

User policy acceptance test ran against fixed case:

go test ./ibm/service/iampolicy/ -run=TestAccIBMIAMUserPolicy_With_Resource_Attributes_Without_Wildcard -timeout 700m -v
...
=== RUN   TestAccIBMIAMUserPolicy_With_Resource_Attributes_Without_Wildcard
--- PASS: TestAccIBMIAMUserPolicy_With_Resource_Attributes_Without_Wildcard (28.01s)
PASS
ok  	github.com/IBM-Cloud/terraform-provider-ibm/ibm/service/iampolicy	30.253s