fix(datepicker): enable showToday prop to be provided on TypeScript

[arthurdenner]

What kind of change does this PR introduce?
Bugfix. Closes #302.

What is the current behavior?
The showToday prop is not listed in the TS types.

What is the new behavior?
The prop is listed and an example of its usage was added to the docs.

Checklist:

• Documentation
• Tests
• Ready to be merged

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[codecov]

Codecov Report

Merging #306 into develop will decrease coverage by 0.05%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           develop     #306      +/-   ##
===========================================
- Coverage    87.84%   87.78%   -0.06%     
===========================================
  Files           15       15              
  Lines          477      475       -2     
  Branches        94       94              
===========================================
- Hits           419      417       -2     
  Misses          56       56              
  Partials         2        2              

Impacted Files	Coverage Δ
src/components/calendar/calendar.tsx	100.00% <ø> (ø)
src/components/icon.tsx	100.00% <ø> (ø)
src/index.tsx	90.67% <ø> (ø)

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[arthurdenner]

🎉 This PR is included in version 2.8.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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