NEWS.md: add release notes for v0.39.0

[jameshcorbett]

Problem: there are no release notes for v0.39.0.

Add them.

Depends on:

• JGF simplification #1293
• Dense resource type with DoS protection #1287

@zekemorton @milroy @trws anything else we should get in by tomorrow?

[trws]

I think that's the list, will go over the JGF simplification shortly, I just set MWP on the Dense resource type PR, because we're actually testing the error report in an old test, will add more to that but I think we need that fix in ASAP and I'm not sure I can get to the addition in a reasonable time.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 75.3%. Comparing base (283b039) to head (d1790aa).
Report is 2 commits behind head on master.

Additional details and impacted files

@@          Coverage Diff           @@
##           master   #1302   +/-   ##
======================================
  Coverage    75.3%   75.3%           
======================================
  Files         111     111           
  Lines       15297   15297           
======================================
  Hits        11529   11529           
  Misses       3768    3768