Tuning parameters of cpimport for implicit invocations

In certain cases standard SQL statements are implicitly converted to cpimport invocations. Examples include LOAD DATA and INSERT INTO... SELECT FROM (both with certain restrictions).

cpimport is known for being highly configurable when invoked from command-line, but during such an implicit invocation there is no configuration that can be used to tune the behaviour of cpimport.

It should be noted that certain parameters have significant impact on the performance of cpimport - e.g., the number of reader/writer threads etc.

This ticket requests the creation of a set of configuration parameters that correspond to cpimport command-line ones which should be used during an implicit invocation of cpimport. If cpimport is made to read such a configuration at start-up, this will also mean that the same preconfigured values will override the built-in defaults when invoking cpimport manually.

At a glance, the most obvious place for such configuration parameters would be ColumnStore.xml (perhaps a new section?). Using MariaDB variables for this might also be possible, although this will mean that configured values will not apply when calling cpimport manually on the command line.