Allow generating presigned URLs for KVS records

[barjin]

Since #453 we can generate presigned URLs for KVS keys and Dataset items.

JS Client can generate presigned URLs for separate KVS records (see getRecordPublicUrl). This method seems to be missing from the Python client.

[barjin]

See apify/apify-client-js#725 for JS implementation.

[Pijukatel]

I think that in Python tooling, this is currently implemented on SDK level. I will move it down to the client level.

[Pijukatel]

Is this documented on the API level @barjin?
I somehow can't find it, for example, here: https://docs.apify.com/api/v2/key-value-store-record-get

[barjin]

Afaik there is no API endpoint for this, you can acquire the signing secret from the https://api.apify.com/v2/key-value-stores/[id] endpoint and then use that to generate the presigned URL locally (see e.g. here).