Azure Key Vault based config

[martinothamar]

Description

Populate config based on Azure KV using default credentials locally and workload identity otherwise. URL is TBD

Related Issue(s)

• Part of Config and setup of the supplier Maskinporten client #7

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)