Add snackbar component

[sarahd93]

Checklist:

• Tests
• CHANGELOG Entry

[codecov]

Codecov Report

Merging #1422 into master will increase coverage by 0.03%.
The diff coverage is 50.94%.

@@            Coverage Diff             @@
##           master    #1422      +/-   ##
==========================================
+ Coverage   35.58%   35.62%   +0.03%     
==========================================
  Files         980      982       +2     
  Lines       21989    22042      +53     
  Branches     6048     6031      -17     
==========================================
+ Hits         7825     7852      +27     
- Misses      12807    12833      +26     
  Partials     1357     1357

Impacted Files	Coverage Δ
gsa/src/stories/snackbar.js	0% <0%> (ø)
gsa/src/web/components/snackbar/snackbar.js	84.37% <84.37%> (ø)

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