Allow to set list of allowed instances at region level

[mzueva]

Background At the moment it is possible to set preferences cluster.allowed.instance.types and cluster.allowed.instance.types.docker as ContextualPreference for user/role/tool or system wide. For some cases it would be also useful to set these preferences for a specific region.

Approach

• User shall be able to set cluster.allowed.instance.types and cluster.allowed.instance.types.docker preferences for cloud region
• Priority of the preferences from highest to lowest: user - role - tool - region - system
• These preferences shall be considered during run launch