Styled file field with materializecss template filter

[zodiacfireworks]

I want to merge this change because in some places of the dashboard we have file fields with material style. But in other places we have an ugly browser based file field. With this little PR we will have file fields with material style using the template filter materializecss.

Screenshots

Picture from product image form:

Picture from category form:

Picture from category form after changes:

Pull Request Checklist

1. Privileged views and APIs are guarded by proper permission checks.
2. All visible strings are translated with proper context.
3. All data-formatting is locale-aware (dates, numbers, and so on).
4. Database queries are optimized and the number of queries is constant.
5. Database migration files are up to date.
6. The changes are tested.
7. The code is documented (docstrings, project documentation).
8. GraphQL schema and type definitions are up to date.
9. Changes are mentioned in the changelog.

[zodiacfireworks]

Hi, I already proposed this change in #3690 but I moved to another branch in order to submit more PRs.

I would appreciate an answer about this little contribution. 😄

[codecov]

Codecov Report

Merging #3998 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #3998   +/-   ##
=======================================
  Coverage   91.29%   91.29%           
=======================================
  Files         267      267           
  Lines       14508    14508           
  Branches     1395     1395           
=======================================
  Hits        13245    13245           
  Misses        894      894           
  Partials      369      369

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[zodiacfireworks]

I updated this PR with the latest commit in master branch

[NyanKiyoshi]

Looks good to me and it works great!

Don't forget to update the changelog!

[zodiacfireworks]

Hi, @NyanKiyoshi

I have updated the change log

[maarcingebala]

@zodiacfireworks Congrats on your first PR to Saleor! 🎉

[zodiacfireworks]

❤️ Thanks! @maarcingebala, @NyanKiyoshi