Hashed-based approach sharding key type

[Denchick]

There is no "HASH" keyword in the "ALTER DISTRIBUTION" command definition. Therefore, when using a key-range-based approach, we use the int64 golang type, but when using a hash-based approach, the underlying type becomes uint32, which leads to confusion.

What should we do?

• Update or documentation
• Introduce new uint type (should be the underlying type uint32 or uint64?)
• Forbid using int type for hash-based approach