feat(lambda-at-edge): no-op rewrite support

[dphang]

Should fix: #733

[codecov]

Codecov Report

Merging #759 into master will increase coverage by 0.03%.
The diff coverage is 91.66%.

@@            Coverage Diff             @@
##           master     #759      +/-   ##
==========================================
+ Coverage   79.66%   79.70%   +0.03%     
==========================================
  Files          55       55              
  Lines        1800     1808       +8     
  Branches      391      394       +3     
==========================================
+ Hits         1434     1441       +7     
- Misses        308      309       +1     
  Partials       58       58              

Impacted Files	Coverage Δ
...ackages/libs/lambda-at-edge/src/default-handler.ts	92.72% <66.66%> (-0.33%)	⬇️
packages/libs/lambda-at-edge/src/api-handler.ts	86.66% <100.00%> (+0.30%)	⬆️
...ckages/libs/lambda-at-edge/src/routing/rewriter.ts	100.00% <100.00%> (ø)

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