make google_iam_workload_identity_pool_provider.oidc updatable

[modular-magician]

Context: b/190760650

Currently, attempting to update fields within oidc gives the error:

googleapi: Error 400: A FieldMask with at least one path must be specified.

There were two problems with updating this field are:

1. oidc was set to input: true while the child fields were not. oidc.allowed_audiences and oidc.issuer_uri were not ForceNew but also not included in the field mask. This lead to the above error
2. ForceNew doesn't work for this resource unless the identity fields are changing. Deleting this resource just sets the status to inactive and when the provider goes to recreate it causes a 409 already existing

To remedy this, I removed input: true on the appropriate fields and added oidc.allowed_audiences and oidc.issuer_uri to the update mask. Also added a test step to use this scenario.

Release Note Template for Downstream PRs (will be copied)

iam: fixed an issue in `google_iam_workload_identity_pool_provider` where `aws` and `oidc` were not updatable.

Derived from GoogleCloudPlatform/magic-modules#4879