Policy blocks API: introduce aliases for fields

[ilyozzz]

During API integration I found that we need to provide POST request body data in format { field0: <>, field1: <>, ..., fieldX: <> }

But in case of PDD creation we're using a policy that requires a lot of top-level and nested fields in such format.

We're querying schema now but It's kind of difficult to keep integrations actual

Maybe it's better to have some kind of aliases for fields?

Inspired by descriptions among fields: https://docs.hedera.com/guardian/guardian/demo-guide/renewable-energy-credits/demo-using-apis#request-body-1