Charge for metadata attribute

[roman-khimov]

Is your feature request related to a problem? Please describe.

I'm always frustrated when additional workload is not payed for in NeoFS. nspcc-dev/neofs-api#309 should be a paid for attribute, just like NNS names.

Describe the solution you'd like

Add a configuration option and charge for this attribute.

[roman-khimov]

The problem is, we don't see attributes at the contract level (at least not until we refactor the container structure).

[roman-khimov]

We can have a different price for meta-enabled containers though. And it'd be even more fair since the overhead increases per-object.