Natural sort order for a string field that may contain numbers

Sort strings using the number value if they contain numbers. Example:

1-1
1-2
1-10
1-11
1-100
2-1
10-1
11-1
100-1
a 1 b 1 c 1 d
a 01 b 1 c 2 d
a 1 b 1 c 10 d

Currently this is sorted character by character:

1-1
1-10
1-100
1-11
1-2
10-1
100-1
11-1
2-1
a 01 b 1 c 2 d
a 1 b 1 c 1 d
a 1 b 1 c 10 d

The natural sort order is also called humanized sort order: https://en.wikipedia.org/wiki/Natural_sort_order
Code examples exist for Postgres: https://stackoverflow.com/questions/12965463/humanized-or-natural-number-sorting-of-mixed-word-and-number-strings

Extend schema.json to allow the index section of a field to allow "naturalSortOrder": true (defaults to false). If true create the index using natural sort order.
Extend cql2pg to use natural sort order for that field if it is in the `sortBy` clause of a CQL query.

Out of scope: Supporting more than one sort order for a given field and picking one of them using a sort modifier in the cql query, for example sortBy poLineNumber/sort.natural and sortBy poLineNumber/sort.string

Suggested SQL function:

CREATE OR REPLACE FUNCTION natural_sort(text, int) RETURNS text AS $$
  -- Return $1 with each sequence of digits expanded to length $2 by prepending leading zeros or
  -- shrunken to length $2 by deleting leading zeros. Other digits get never deleted.
  SELECT regexp_replace(
    regexp_replace($1, '\d+', repeat('0', $2 - 1) || '\&', 'g'),
    '0*(\d{' || $2 || ',})', '\1', 'g')
$$ LANGUAGE sql IMMUTABLE STRICT PARALLEL SAFE; 

This function does not truncate numbers that exceed the max length configured by $2.

RMB currently supports sqlExpression and sqlExpressionQuery but it doesn't support them in the sortBy clause.