Make contributor data available to hugo

[imorente]

- Summary

Adds a gulp task to convert the .all-contributorsrc json file into yaml, and copies it to website's data folder so hugo can use it.

- Test plan

cd website && yarn install && yarn build

There should be a website/site/data/contributors.yml than can then be used in a hugo template. Eg. The following code would output a list of with all the contributors' names.

  {{ range .Site.Data.contributors }}
    <ul>
    {{ range . }}
      <li>{{ .name }}</li>
    {{ end }}
  {{ end }}

- Description for the changelog

- A picture of a cute animal (not mandatory but encouraged)

[verythorough]

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[imorente]

this PR was closed on purpose. The change was merged into master via #880