feat(publisher-ers): support customizable artifact extensions

[nullxx]

• I have read the contribution documentation for this project.
• I agree to follow the code of conduct that this project follows, as appropriate.
• The changes are appropriately documented (if applicable).
• The changes have sufficient test coverage (if applicable).
• The testsuite passes successfully on my local machine (if applicable).

Summarize your changes:
Now, when using publisher electron-release-server you can select the file extensions of the artifacts to upload.
This is configurable.

Fixes ArekSredzki/electron-release-server#239

[codecov]

Codecov Report

Merging #2220 (936fab5) into master (e1c218c) will decrease coverage by 0.51%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master    #2220      +/-   ##
==========================================
- Coverage   72.66%   72.15%   -0.52%     
==========================================
  Files          74       74              
  Lines        2221     2237      +16     
  Branches      420      427       +7     
==========================================
  Hits         1614     1614              
- Misses        448      464      +16     
  Partials      159      159              

Impacted Files	Coverage Δ
...lisher/electron-release-server/src/PublisherERS.ts	21.95% <0.00%> (-5.33%)	⬇️

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