fix(lambda-at-edge): properly copy node_modules in serverless-trace mode for regeneration lambda

[dphang]

• This wasn't working properly since copyTraces() was always copying to the default lambda directory. We need to pass in the directory.
• Won't add tests since serverless-trace is already getting deprecated as of later Next.js versions (e.g 10.2.3) but manually tested.

Related: #1098

[codecov]

Codecov Report

Merging #1319 (a72fc81) into master (f842e67) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1319   +/-   ##
=======================================
  Coverage   83.61%   83.61%           
=======================================
  Files          97       97           
  Lines        3345     3345           
  Branches     1001     1001           
=======================================
  Hits         2797     2797           
  Misses        486      486           
  Partials       62       62           

Impacted Files	Coverage Δ
packages/libs/lambda-at-edge/src/build.ts	97.09% <ø> (ø)

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