feat(server): proxyconfig callback args

[RavenHursT]

• This is a bugfix
• This is a feature
• This is a code refactor
• This is a test update
• This is a docs update
• This is a metadata update

For Bugs and Features; did you add new tests?

yes

Motivation / Use-Case

This allows configuration of the proxy to be dynamic based off the Express req, res, and next args.

#2360 (comment)

Breaking Changes

None

[jsf-clabot]

Thank you for your submission, we really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.

[codecov]

Codecov Report

Merging #2369 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master    #2369   +/-   ##
=======================================
  Coverage   93.95%   93.95%           
=======================================
  Files          34       34           
  Lines        1291     1291           
  Branches      368      368           
=======================================
  Hits         1213     1213           
  Misses         77       77           
  Partials        1        1

Impacted Files	Coverage Δ
lib/Server.js	97.33% <100%> (ø)	⬆️

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[alexander-akait]

Will be great to have test where we check req, res and next (for example simple integration test)

[hiroppy]

Thank you for your contribution. closed via #2714