refactor: update loading | adjust notification component

[mlmoravek]

This is part of #606

In this PR I refactored the loading component from Options-API to Composition-API.

Fixes #608

Proposed Changes

• Update Loading to composition api
• Add label prop to notification component
• Update docs
• Adjust Notification component

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[codecov]

Codecov Report

All modified lines are covered by tests ✅

Comparison is base (6da9426) 63.89% compared to head (dff1e18) 63.39%.
Report is 2 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #622      +/-   ##
===========================================
- Coverage    63.89%   63.39%   -0.50%     
===========================================
  Files           85       86       +1     
  Lines         5495     5532      +37     
  Branches      1561     1566       +5     
===========================================
- Hits          3511     3507       -4     
- Misses        1873     1914      +41     
  Partials       111      111              

Flag	Coverage Δ
oruga	65.92% <ø> (ø)
oruga-next	51.99% <ø> (-2.41%)	⬇️

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see 3 files with indirect coverage changes

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