Update sorting query operator to take multiple fields

[munrojm]

This PR incorporated multi field sorting into the sorting query operator.

[codecov]

Codecov Report

Merging #500 (aa019ba) into main (25ad553) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #500   +/-   ##
=======================================
  Coverage   88.44%   88.44%           
=======================================
  Files          40       40           
  Lines        2657     2658    +1     
=======================================
+ Hits         2350     2351    +1     
  Misses        307      307           

Impacted Files	Coverage Δ
src/maggma/api/query_operator/sorting.py	100.00% <100.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 25ad553...aa019ba. Read the comment docs.

[lgtm-com]

This pull request introduces 2 alerts when merging aa019ba into 25ad553 - view on LGTM.com

new alerts:

• 1 for Unused import
• 1 for Non-iterable used in for loop