Add hugo and git to webhook image

[priyawadhwa]

Adding hugo and git to the skaffold image will allow the webhook to
deploy it and:

1. Use git to clone a user's branch with docs changes
2. Use hugo to set up a static website which will show those changes

[r2d4]

Don't you want this in https://github.com/GoogleContainerTools/skaffold/blob/master/deploy/webhook/Dockerfile?

[priyawadhwa]

It could go there as well! Basically we just need an image for the docs controller to deploy which has git and hugo, but I think the skaffold image makes sense because hugo is needed there for #1060 as well

[codecov-io]

Codecov Report

Merging #1226 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1226   +/-   ##
=======================================
  Coverage   41.49%   41.49%           
=======================================
  Files          95       95           
  Lines        4234     4234           
=======================================
  Hits         1757     1757           
  Misses       2307     2307           
  Partials      170      170

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[r2d4]

The skaffold image shouldn't have hugo. It's made to be minimal and only have the dependencies for skaffold

[priyawadhwa]

For sure, moved to the webhook image