feat(lambda-at-edge): support fallback: false for getStaticPaths and fix cache-control header

[dphang]

Fixes/closes: #673

Also adds proper cache-control header so that CloudFront can cache the responses including the 404 page.

[codecov]

Codecov Report

Merging #681 into master will decrease coverage by 0.11%.
The diff coverage is 69.23%.

@@            Coverage Diff             @@
##           master     #681      +/-   ##
==========================================
- Coverage   79.29%   79.17%   -0.12%     
==========================================
  Files          52       52              
  Lines        1608     1618      +10     
  Branches      338      345       +7     
==========================================
+ Hits         1275     1281       +6     
  Misses        277      277              
- Partials       56       60       +4     

Impacted Files	Coverage Δ
...ackages/libs/lambda-at-edge/src/default-handler.ts	94.39% <69.23%> (-1.55%)	⬇️

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