Threaded dnsresolve module

[TheTechromancer]

No description provided.

[codecov-commenter]

Codecov Report

Merging #1535 (152464e) into master (f2a3acd) will increase coverage by 0.00%.
The diff coverage is 33.33%.

@@           Coverage Diff           @@
##           master    #1535   +/-   ##
=======================================
  Coverage   53.69%   53.70%           
=======================================
  Files         475      475           
  Lines       39868    39875    +7     
=======================================
+ Hits        21409    21414    +5     
- Misses      18459    18461    +2     

Impacted Files	Coverage Δ
modules/sfp_dnsresolve.py	39.87% <33.33%> (+0.68%)	⬆️

---

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 f2a3acd...152464e. Read the comment docs.

[Omicron166]

Legit pull request, should work fine

[Omicron166]

@smicallef this pr looks good, pls check it

[smicallef]

Similar to my sfp_commonsrv feedback, can we make the number of threads here configurable in the same way other modules do it? A default hard-coded setting of 20 is likely too high for many systems considering how threading-intensive SpiderFoot already is these days.