Added support for nested messages in protobuf output format

[vitlibar]

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For changelog. Remove if this is non-significant change.

Category (leave one):

• Improvement
• Performance Improvement

This PR adds support for nested messages in the format schema, making possible to output protobuf messages with schema like this:

message MessageType {
  message XType {
    message YType {
      int32 z;
    };
    repeated YType y;
  };
  XType x;
};

This PR also improve performance of writing protobuf messages.

[vitlibar]

I've measured the performance:

SELECT * FROM datasets.hits_v1 FORMAT TSV            33.16 real    28.67 user     4.05 sys
SELECT * FROM datasets.hits_v1 FORMAT Protobuf       38.18 real    34.59 user     3.32 sys
SELECT * FROM datasets.hits_v1 FORMAT JSONEachRow    58.02 real    47.56 user     8.97 sys