v.1.5.1

• add Attribute Authority sample reference implementation
• add Attribute Authority OpenAPI document (/attribute-authority/openapi)
• add Attribute Authority OpenAPI online documentation based on Redocly (/attribute-authority/apidoc)
• add Attribute Authority Entity Federation endpoint (/attribute-authority/.well-known/openid-federation)
• add Attribute Authority test case (rich authentication request for grant token)