Update KVOperations v2 maths operations

[maoueh]

Update the KVOperations to reflect the following model.

message KVOperations {
  repeated KVOperation operations = 1;
}

message KVOperation {
  string key = 1;
  bytes value = 2;
  oneof value {
    string string = 1;
    bytes bytes = 2;
    uint64 uint64 = 3;
    int64 int64 = 4;
    uint32 uint32 = 5;
    int32 int32 = 6;
    string bigint = 7;
    string bigdecimal = 8;
    bool bool = 9;
  }
  Op op = 3;
  enum Op {
    UNSET = 0;
    SET = 1;
    DELETE = 2;
    ADD = 3;
    MAX = 4;
    MIN = 5;
  }
}

• Update Proto & KV Sink operation
• Update example in block_meta substreams