Container consistency policy

[roman-khimov]

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

I'm always frustrated when we can't specify consistency policy for a container.

Describe the solution you'd like

Add an optional enum field with the following options:

• available (just like the old one, no meta)
• strict (nodes use meta and wait for meta acceptance)
• optimistic (nodes use meta, but do not wait for acceptance)

Describe alternatives you've considered

If we want to alternate between different modes and preserve compatibility, there are not a lot of them.

[roman-khimov]

CC @EESergey. This can be an attribute.