Move code from markdown to snippets

[martintmk]

Details on the issue fix or feature implementation

• This PR introduces https://github.com/SimonCropp/MarkdownSnippets to dynamically add code to markdowns.
• Validation of all links in cake. (fails the build if links are wrong)
• Docs are automatically updated on every push to main branch by creating a PR (see Update the code-snippets in the documentation #1545)

Contributes to #1091

Confirm the following

• I started this PR by branching from the head of the default branch
• I have targeted the PR to merge into the default branch
• I have included unit tests for the issue/feature
• I have successfully run a local build

[martincostello]

Maybe it would be better to reference these from source rather than NuGet? Then if new features are added in the future, you can add docs in the same PR, rather than having to wait until it's been published.

[martintmk]

I was thinking about this, but it would require adding sources to Samples project and based on ou current flow we are updating the code after the nuget is pushed anyway.

Alternatively, move Snippets under src folder?

[martincostello]

Yeah I think moving the snippets somewhere else is better, as even though we might be doing lots of work now, post v8 it's probably going to be much less frequent in terms of pushes to NuGet.

[martintmk]

Are you fine putting them in src/Snippets ?

[martincostello]

Sure.

[codecov]

Codecov Report

Patch and project coverage have no change.

Comparison is base (937bf26) 83.92% compared to head (2f8a4b7) 83.92%.
Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1540   +/-   ##
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  Coverage   83.92%   83.92%           
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  Files         279      279           
  Lines        6518     6518           
  Branches     1017     1017           
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  Hits         5470     5470           
  Misses        839      839           
  Partials      209      209           

Flag	Coverage Δ
linux	83.92% <ø> (ø)
macos	83.92% <ø> (ø)
windows	83.92% <ø> (?)

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[martincostello]

Nice work