Create Resource For OAuth Client App Role Assignments

[tgoodsell-tempus]

This is a new resource to allow the assignment of admin roles on OAuth Clients in Okta. Note this feature may be behind a feature flag in your org depending on it's version and other settings.

API reference: https://developer.okta.com/docs/api/openapi/okta-oauth/oauth/tag/RoleAssignment/

Adding to the manual SDK for now since the Okta Golang SDK does not yet have these API calls supported.

Ref: #1662

[tgoodsell-tempus]

This one is also complete on my end.

[tgoodsell-tempus]

@monde @duytiennguyen-okta Just tagging you to ensure you know I am looking for a review (and eventual approval) on adding this resource.

[monde]

@tgoodsell-tempus - @duytiennguyen-okta and I will do a review and give feedback. Thanks for the work.

[duytiennguyen-okta]

lgtm. @tgoodsell-tempus I will have to bring the commit in manually to

1. Record a vcr on this
2. There is change in the example folder and newFixtureManager that will cause an error on this PR

accident

[tgoodsell-tempus]

lgtm. @tgoodsell-tempus I will have to bring the commit in manually to

1. Record a vcr on this
2. There is change in the example folder and newFixtureManager that will cause an error on this PR

@duytiennguyen-okta @monde Cheers! I had originally looked into the VCR record and such myself, however the VCR recording was not yet implemented on the "framework provider" models. I would be interested in getting that sorted out as well as switching this repo to the new testing library (instead of the SDKv2 testing library): https://github.com/hashicorp/terraform-plugin-testing