fix(lambda-at-edge): non-dynamic pages (SSG, SSR) should be prioritized over dynamic fallback pages

[dphang]

• When fallback pages for dynamic routes are used, it shouldn't interfere with SSG and SSR pages - those should take precedence as defined here: https://nextjs.org/docs/routing/dynamic-routes#caveats

Tests

Added e2e tests to ensure this doesn't break.

[codecov]

Codecov Report

Merging #685 into master will increase coverage by 0.03%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #685      +/-   ##
==========================================
+ Coverage   79.25%   79.29%   +0.03%     
==========================================
  Files          52       52              
  Lines        1615     1618       +3     
  Branches      344      345       +1     
==========================================
+ Hits         1280     1283       +3     
  Misses        277      277              
  Partials       58       58              

Impacted Files	Coverage Δ
...ackages/libs/lambda-at-edge/src/default-handler.ts	95.23% <100.00%> (+0.06%)	⬆️

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