Added caching of decision request response

[HenningNormann]

Description

The udir performance test case triggers 65 decision requests. With caching of the decision request response the number of requests is reduced to 4.

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)

[jonkjetiloye]

The PEP has no context of the state of an instance. So caching the result based on the request alone is not sufficient and can lead to false positives.