feat: checkbox-group component

[olkeoguz]

Includes:

• checkbox-group component of which the implementation was discussed in Using checkbox component in form #291:

 <bl-checkbox-group id="sportSelection" label="Choose sports you like" name="sports" required value='["basketball","tennis"]'>
  <bl-checkbox value="football">Football</bl-checkbox>
  <bl-checkbox value="basketball">Basketball</bl-checkbox>
  <bl-checkbox value="tennis">Tennis</bl-checkbox>
</bl-checkbox-group>

<script>
  sportSelection.value; // ['basketball', 'tennis']
</script>

• accessibility and form control improvements of checkbox component mentioned in Accessibility improvements on Checkbox component #290,

checkbox focus state screenshots will be added after #322 resolves.

Closes #290, closes #291.

[muratcorlu]

Looks very good! I just have a small remark. And let's also ask for a design review from @buseselvi 😊

[olkeoguz]

After searching and discussing checkbox-group examples with @buseselvi, we decided to change the keyboard navigation. Pressing tab will always switch to the next element in the group rather than focusing outward.
Example : https://developer.mozilla.org/en-US/docs/Web/HTML/Element/input/checkbox

But navigating with arrow keys will be the same as now.
I'll make these changes shortly if that's final @muratcorlu @buseselvi .

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

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[github-actions]

🎉 This PR is included in version 2.0.0-beta.50 🎉

The release is available on:

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

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[github-actions]

🎉 This PR is included in version 2.0.0 🎉

The release is available on:

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

Your semantic-release bot 📦🚀