feat: Adds support for OIDC WORKLOAD IdP type to federated_settings_identity_provider

[EspenAlbert]

Description

Adds support for OIDC Workload IdPs for mongodbatlas_federated_settings_identity_provider

Link to any related issue(s): CLOUDP-250915

Type of change:

• Bug fix (non-breaking change which fixes an issue). Please, add the "bug" label to the PR.
• New feature (non-breaking change which adds functionality). Please, add the "enhancement" label to the PR. A migration guide must be created or updated if the new feature will go in a major version.
• Breaking change (fix or feature that would cause existing functionality to not work as expected). Please, add the "breaking change" label to the PR. A migration guide must be created or updated.
• This change requires a documentation update
• Documentation fix/enhancement

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Further comments

[github-actions]

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[marcosuma]

might be irrelevant, but should we have WORKLOAD somewhere?

[oarbusi]

In the model methods there isn't any kind of validation of the values, so I think it's okay to not test different values for idp_type

[erabil-mdb]

LGTM!