Support directly ingest exported SST files

[v0y4g3r]

What type of enhancement is this?

Performance

What does the enhancement do?

Optimize COPY FROM execution if the source schema matches destination schema by directly copy source files into region directory.

Implementation challenges

Files exported by COPY TO statements do not contain sequence and op type fields, we need to make some changes to query engine to allow such situation by treating missing op type as PUT and sequence as some value that is "always not equal to any other sequence number".