feat(addon-notes): use @storybook/router <Link> to render links in notes

[sto3psl]

Issue: #6394

What I did

Links in the notes addon cause storybook to reload. This is not the best user experience when the link points to a different story. Since storybook uses a client side router already, I used the overrides option in markdown-to-jsx to use a custom <NotesLink /> component for all markdown links. It basically uses normal <a> tags for absolute links (external) and the @storybook/router <Link />
for internal links (relative). That way, nothing breaks and storybook uses the @reach/router in addon notes when it can.

How to test

• Is this testable with Jest or Chromatic screenshots?
  Yes, I added tests and an example in the svelte kitchen sink app.
• Does this need a new example in the kitchen sink apps?
  I added a relative link in the svelte kitchen sink app but this is nothing where users have to do anything different.
• Does this need an update to the documentation?
  No.

If your answer is yes to any of these, please make sure to include it in your PR.

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[codecov]

Codecov Report

Merging #6398 into next will increase coverage by 0.03%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##             next    #6398      +/-   ##
==========================================
+ Coverage   38.31%   38.35%   +0.03%     
==========================================
  Files         649      649              
  Lines        9857     9863       +6     
  Branches      388      389       +1     
==========================================
+ Hits         3777     3783       +6     
  Misses       6020     6020              
  Partials       60       60

Impacted Files	Coverage Δ
addons/notes/src/Panel.tsx	50% <100%> (+7.14%)	⬆️

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[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (next@8aae29d). Click here to learn what that means.
The diff coverage is 100%.

@@           Coverage Diff           @@
##             next    #6398   +/-   ##
=======================================
  Coverage        ?   40.85%           
=======================================
  Files           ?      616           
  Lines           ?     8523           
  Branches        ?      536           
=======================================
  Hits            ?     3482           
  Misses          ?     4949           
  Partials        ?       92

Impacted Files	Coverage Δ
addons/notes/src/Panel.tsx	38.88% <100%> (ø)

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Δ = absolute <relative> (impact), ø = not affected, ? = missing data
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[ndelangen]

Awesome!