SAML identity provider shows changes on every run due to ActiveEncryptionCertificate

[liamfit]

Great module!

I am using this to create a SAML identity provider in my user pool like this:

  identity_providers = [
    {
      provider_name = "myOrgGoogle"
      provider_type = "SAML"
      provider_details = {
        IDPInit               = false
        IDPSignout            = false
        EncryptedResponses    = false
        SSORedirectBindingURI = "https://accounts.google.com/o/saml2/idp?idpid=xxxx"
        MetadataFile          = file("../../files/google_saml_metadata.xml")
      }
  ]

When running terraform plan I always see changes to provider_details. If I change identity_providers variable to sensitive = false then I can see that ActiveEncryptionCertificate is being changed from null to the encryption cert generated for my user pool:

  # module.cognito.aws_cognito_identity_provider.identity_provider[0] will be updated in-place
  ~ resource "aws_cognito_identity_provider" "identity_provider" {
        id                = "eu-west-2_hrcJfpRjv:ThriveGoogle"
      ~ provider_details  = {
          - "ActiveEncryptionCertificate" = "MIICvDCCAaSgAwIBAgII....." -> null
            # (5 unchanged elements hidden)
        }
        # (5 unchanged attributes hidden)
    }

Plan: 0 to add, 1 to change, 0 to destroy.

If I add this value to provider_details then the plan shows no changes but as it's different value for every user pool it's a bit of a pain to add this to every environment. Also, according to the docs these signing and encryption certs get regenerated every year so it's gonna be a bit of a pain to maintain:
https://docs.aws.amazon.com/cognito/latest/developerguide/cognito-user-pools-SAML-signing-encryption.html

Looks like I can get the current signing certificate with this data source but not the encryption cert:
https://registry.terraform.io/providers/hashicorp/aws/latest/docs/data-sources/cognito_user_pool_signing_certificate

I'm wondering if the best thing to do is add provider_details to the ignore_changes lifecycle block as was done with schemas here:
#130