Declaration payload key changer API

[jessepeterson]

Yes, you can just re-upload a declaration with a changed key. But it might be nice to send an API request with just a key to set in the declaration's payload. Particularly for property management declarations (where the whole point is just a set of key/values pairs.). This would either need to block on the 'special' keys in some payloads (like how we figure out declaration references now) or re-compute declaration references for special keys and update the DB.

As a related off-shoot of this consider an API/function for something like "add declaration to existing activation". Technically this is just modifying the array in an activation declaration's StandardConfigurations key so may be this same feature 🤷.