expose AWS_REGION_NAME in S3FeedStorage

[BurnzZ]

Similar PRs:

• Use AWS_REGION_NAME and AWS_ENDPOINT_URL, if available, for S3 feed export #5092
• fix #2448 : add aws region support  #4429
• fix #2448:add s3 region support #4417

[codecov]

Codecov Report

Merging #5980 (1724a77) into master (7522aee) will decrease coverage by 0.07%.
The diff coverage is 100.00%.

❗ Current head 1724a77 differs from pull request most recent head a689fe5. Consider uploading reports for the commit a689fe5 to get more accurate results

@@            Coverage Diff             @@
##           master    #5980      +/-   ##
==========================================
- Coverage   89.21%   89.14%   -0.07%     
==========================================
  Files         162      162              
  Lines       11302    11303       +1     
  Branches     1835     1835              
==========================================
- Hits        10083    10076       -7     
- Misses        927      933       +6     
- Partials      292      294       +2     

Impacted Files	Coverage Δ
scrapy/extensions/feedexport.py	93.33% <100.00%> (-2.31%)	⬇️