docs: add documentation for using portal service accounts

[scottd018]

What this PR does / why we need it:

There is currently no information on using the client_id and client_secret parameters when using portal service accounts. This creates confusion when customers are trying to use the access tokens, described at https://docs.redhat.com/en/documentation/red_hat_customer_portal/1/html/creating_and_managing_service_accounts/ref-ciam-svc-acct-api-creating-service-acct, and causes a timeout when provisioning clusters, which is hard-coded at 15 minutes.

Which issue(s) this PR fixes (optional, use fixes #<issue_number>(, fixes #<issue_number>, ...) format, where issue_number might be a GitHub issue, or a Jira story (OCM-xxxx): Fixes #

Change type

• [ ] New feature
• [ ] Bug fix
• [ ] Build
• [ ] CI
• [x] Documentation
• [ ] Performance
• [ ] Refactor
• [ ] Style
• [ ] Unit tests
• [ ] Subsystem tests

Checklist

• [x] Subject and description added to both, commit and PR.
• [x] Relevant issues have been referenced.

[openshift-ci[bot]]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[openshift-ci[bot]]

Hi @scottd018. Thanks for your PR.

I'm waiting for a terraform-redhat member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[marcolan018]

@hunterkepley Please help to review this pr, which adds the missing part for the tf, thanks