Bugs in external idp provider_details

[thecaffiend]

In the method _construct_saml_provider_details (in capemeta.py), we have a couple of bugs:

1. The first is that pulumi can show changes in provider_details even when no change has been made. This can be seen in pulumi preview --diff.
2. The second is in the code below. Note that the provider_details dict is initiall set to a value, but then is overwritten in the if and else clauses (it should be updated with the new keys instead)

        # NOTE: CAPE doesn't support IdP initiated SAML at this time
        provider_details = {"IDPInit": "false"}

        if mdfile:  # metadata file
            # according to the AWS docs, the provider details for a metadata
            # document needs plaintext xml with quotes backslash escaped...
            # https://docs.aws.amazon.com/cognito-user-identity-pools/latest/APIReference/API_CreateIdentityProvider.html#API_CreateIdentityProvider_RequestSyntax
            et = ElementTree.parse(mdfile)
            xmlcontent = ElementTree.tostring(et.getroot())
            escaped_xml = xmlcontent.decode("utf-8").replace('"', '"')
            provider_details = {"MetadataFile": escaped_xml}
        # NOTE: using else here made the typechecker unhappy
        elif mdurl:  # metadata url
            provider_details = {"MetadataURL": mdurl}

        return provider_details