Support `LOAD DATA LOCAL INFILE` command for MySQL

[telezhnaya]

BULK INSERT support is limited, people have to write the code like this
#294 (comment)

So I decided to load the data from files.
And, as I see, there's no support for load data local infile 😔

sqlx/sqlx-core/src/mysql/connection/executor.rs

Line 129 in 593364f

// Ok, Err, ResultSet, or (unhandled) LocalInfileRequest