feat(checkbox): add outline on focus

[yggg]

Please read and mark the following check list before creating a pull request:

• I read and followed the CONTRIBUTING.md guide.
• I read and followed the New Feature Checklist guide.

Short description of what this resolves:

Adds visual representation of focus.

[codecov]

Codecov Report

Merging #731 into master will decrease coverage by 0.01%.
The diff coverage is 60%.

@@           Coverage Diff            @@
##           master   #731      +/-   ##
========================================
- Coverage   76.01%    76%   -0.02%     
========================================
  Files         192    192              
  Lines        5291   5296       +5     
  Branches      399    399              
========================================
+ Hits         4022   4025       +3     
- Misses       1184   1186       +2     
  Partials       85     85

Impacted Files	Coverage Δ
...rk/theme/components/checkbox/checkbox.component.ts	89.47% <60%> (-4.47%)	⬇️