tests: test1: add test cases for json_object_array_insert_idx()

tests: test1: add test cases for json_object_array_insert_idx()

This change adds a few test cases to test the behavior of the new
json_object_array_insert_idx() function, to make sure it behaves according
to specification in doc-string.

This test uses assert() vs the old method of comparing outputs.
This will cause the test to fail because the outputs won't match, since the
assert() will kick in.

Signed-off-by: Alexandru Ardelean <ardeleanalex@gmail.com>