[opt](parquet) change parquet init footer read size to 48KB (#46904)

### What problem does this PR solve?

Change the initial footer read size from 128KB to 48KB, to slightly
reduce the read size.
This is same as presto/trino, because typically, a 1GB parquet file
usually has footer with size 30~40KB.

And usercase shows when there are 30 thousands parquet file, the parse
footer time can reduce from:

```
ParseFooterTime:  avg  2s28ms,  max  3s707ms,  min  905.866ms
```
to
```
ParseFooterTime:  avg  886.364ms,  max  1s734ms,  min  391.846ms
```

be/src/vec/exec/format/parquet/parquet_thrift_util.h

@@ -34,7 +34,7 @@ namespace doris::vectorized {
 
 constexpr uint8_t PARQUET_VERSION_NUMBER[4] = {'P', 'A', 'R', '1'};
 constexpr uint32_t PARQUET_FOOTER_SIZE = 8;
-constexpr size_t INIT_META_SIZE = 128 * 1024; // 128k
+constexpr size_t INIT_META_SIZE = 48 * 1024; // 48k
 
 static Status parse_thrift_footer(io::FileReaderSPtr file, FileMetaData** file_metadata,
                                   size_t* meta_size, io::IOContext* io_ctx) {