UX-263 Adds Button variant prop

[jonambas]

What Changed

• Adds a new variant prop to Button
• Deprecates the old props outline outlineBorder flat
• Updates the components, and playroom snippets, that used the old props
  • Will update the site in another ticket

How To Test or Verify

• Run storybook and visit - http://localhost:9001/?path=/story/action-button--variants
• Check http://localhost:9001/?path=/story/action-button--deprecated-variants still works

PR Checklist

• Add the correct type label
• Pull request approval from #uxfe or #design-guild

[codecov]

Codecov Report

Merging #573 into rc/4.1.0 will increase coverage by 0.01%.
The diff coverage is 96.15%.

@@             Coverage Diff              @@
##           rc/4.1.0     #573      +/-   ##
============================================
+ Coverage     93.36%   93.38%   +0.01%     
============================================
  Files           128      128              
  Lines          1688     1692       +4     
============================================
+ Hits           1576     1580       +4     
  Misses          112      112              

Impacted Files	Coverage Δ
...kages/matchbox/src/components/DatePicker/Navbar.js	100.00% <ø> (ø)
packages/matchbox/src/components/Drawer/Header.js	100.00% <ø> (ø)
packages/matchbox/src/components/Page/Page.js	89.65% <ø> (ø)
...s/matchbox/src/components/Pagination/Pagination.js	94.87% <0.00%> (ø)
packages/matchbox/src/components/Tabs/Tabs.js	88.57% <ø> (ø)
packages/matchbox/src/components/Button/Button.js	100.00% <100.00%> (ø)
packages/matchbox/src/components/Button/styles.js	100.00% <100.00%> (ø)

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[logansparlin]

Looks good!