[now-static-build] Add hugo, zola, and gutenberg versioning

[styfle]

This PR adds support for build environment variables which enables the user to select which version of Hugo, Zola or Gutenberg they wish to use.

• HUGO_VERSION
• ZOLA_VERSION
• GUTENBERG_VERSION

[codecov-io]

Codecov Report

Merging #3025 into canary will increase coverage by 0.72%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           canary    #3025      +/-   ##
==========================================
+ Coverage   11.33%   12.05%   +0.72%     
==========================================
  Files         267      267              
  Lines       10032    10126      +94     
  Branches     1308     1290      -18     
==========================================
+ Hits         1137     1221      +84     
- Misses       8803     8812       +9     
- Partials       92       93       +1

Impacted Files	Coverage Δ
src/util/metrics.ts	68.18% <0%> (-2.41%)	⬇️
src/util/projects/get-project-by-id-or-name.ts	28.57% <0%> (+3.57%)	⬆️
src/util/get-files.ts	91.66% <0%> (+3.88%)	⬆️
src/util/prefer-v2-deployment.ts	61.9% <0%> (+5.65%)	⬆️
src/util/output/create-output.ts	43.58% <0%> (+12.33%)	⬆️

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[TooTallNate]

Curious why env vars instead of using the config object of the build spec. Is it because of zero config?

[styfle]

Curious why env vars instead of using the config object of the build spec. Is it because of zero config?

@TooTallNate Yes. Users of static site generators will not define the builds key and therefore, cannot assign build configs. In fact, I don't think we are adding any new config options going forward due to zero config.