IAM: Escape SAML metadata XML document when creating a SAML provider

[infame-io]

G'day,

When passing an XML document the characters in the XML are causing the response value to return with a different value.

Error: reading IAM SAML Provider (arn:aws:iam::123456789012:saml-provider/sso-test): operation error IAM: GetSAMLProvider, https response error StatusCode: 200, RequestID: aZ44KsVPnA1fs9yDDYUHUddNxQrOiUyu8scM4elFE6CUdtCNCI1O, deserialization failed, failed to decode response body, expected value for SAMLMetadataDocument element, got xml.StartElement type {{urn:oasis:names:tc:SAML:2.0:metadata EntityDescriptor} [{{ xmlns} urn:oasis:names:tc:SAML:2.0:metadata} {{xmlns saml} urn:oasis:names:tc:SAML:2.0:assertion} {{xmlns ds} http://www.w3.org/2000/09/xmldsig#} {{ entityID} urn:amazon:webservices} {{ validUntil} 2025-08-30T00:00:00Z}]} instead

Sample metadata included to replicate the issue.

Terraform v1.9.5
on darwin_arm64
+ provider registry.terraform.io/hashicorp/aws v5.66.0

[bblommers]

LGTM - thank you for the fix @infame-io!

[github-actions]

This is now part of moto >= 5.0.15.dev8