Feature/xacmlvalidation

[TheTechArch]

Description

Related Issue(s)

• #{issue number}

Verification

• Your code builds clean without any errors or warnings
• Manual testing done (required)
• Relevant automated test added (if you find this hard, leave it and we'll help out)
• All tests run green

Documentation

• User documentation is updated with a separate linked PR in altinn-studio-docs. (if applicable)

[Alxandr]

This isn't really xacml-validation, but xml validation. Do we also want to validate the xacml?