aws_transfer_server::identity_provider_type causes replacement

Description

This is more of a bug than an enhancement but the bug template did not fit either.

AWS Transfer Family now supports changing identity_provider_type without replacement (announced Oct 24, 2025: https://aws.amazon.com/about-aws/whats-new/2025/10/aws-transfer-family-changing-idp-type/).

The Terraform provider still has ForceNew: true on this attribute at internal/service/transfer/server.go:L155, forcing unnecessary server recreation.

Proposal:

Remove ForceNew: true from identity_provider_type to allow in-place updates:

 "identity_provider_type": {
     Type:             schema.TypeString,
     Optional:         true,
-    ForceNew:         true,
     Default:          awstypes.IdentityProviderTypeServiceManaged,
     ValidateDiagFunc: enum.Validate[awstypes.IdentityProviderType](),
 },

### Affected Resource(s) or Data Source(s)

aws_transfer_server::identity_provider_type causes replacement

### Potential Terraform Configuration

```hcl

References

• AWS announcement: https://aws.amazon.com/about-aws/whats-new/2025/10/aws-transfer-family-changing-idp-type/
  • AWS API docs: https://docs.aws.amazon.com/transfer/latest/userguide/configuring-servers-edit-custom-idp.html

Would you like to implement the enhancement?

No