#1812 Add !fs utils getmerge support

[allwefantasy]

What changes were proposed in this pull request?

Test Script:

load delta.`python_data.vega_datasets` as vega;
save overwrite vega as csv.`/tmp/vega` where fileNum="4" and header="true";

!fs -rm /tmp/output.csv;
-- !fs utils getmerge "/tmp/vega/*.csv"  /tmp/output.csv 1
!fs utils getmerge _ -source "/tmp/vega/*.csv"  -target /tmp/output.csv -skipNLines 1;

load  csv.`/tmp/output.csv` where header="true" as tt;
-- select count(*) from vega as output;
select count(*) from tt as output;

How was this patch tested?

Manually

Are there and DOC need to update?

Spark Core Compatibility

ALL