HPCC-9507 Add STD.STR.REPEAT(text, n)

Returns a string containing text repeated n times.

 * @param text          The string to be repeated.
 * @param n             Number of repetitions.
 * @return              A string containing n concatenations of the string text.

Signed-off-by: jamienoss <james.noss@lexisnexis.com>