Randomize port used for function discovery to reduce race conditions.

[taeold]

When spinning up admin server for function discovery, we rely on portfinder.getPort() function to find an open port for the admin server to listen.

portfinder starts from a base port number (e.g. 9005), trying incrementally larger number until an open port is found. This mechanism can lead to race condition when multiple processes look for an open port from the same base port number.

This PR adds a small jitter to the base port number when calling portfinder to reduce likeliness of a race condition.

Fixes #5418.

[codecov-commenter]

Codecov Report

Base: 56.43% // Head: 56.43% // No change to project coverage 👍

Coverage data is based on head (a960c76) compared to base (d4a2ce8).
Patch coverage: 33.33% of modified lines in pull request are covered.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #5444   +/-   ##
=======================================
  Coverage   56.43%   56.43%           
=======================================
  Files         313      313           
  Lines       21232    21232           
  Branches     4333     4333           
=======================================
  Hits        11983    11983           
  Misses       8211     8211           
  Partials     1038     1038           

Impacted Files	Coverage Δ
src/deploy/functions/runtimes/node/index.ts	40.62% <33.33%> (ø)

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