Removed netcoreapp3.1, net5.0 and net6.0 + added net8.0 support

[armanossiloko]

• Removed support for netcoreapp3.1 as it's officially out of support
• Removed support for net5.0
• Added net8.0 support
• Recreated the Middleware sample projects

[armanossiloko]

@khellang Did you plan on migrating your middleware repo to net8.0 and should I go on and close the PR if you prefer to keep things as they are?

[khellang]

Thanks for the contribution! 🙏🏻 Just a few nits from me 😄

[khellang]

Looks like the build failed because GitHub Actions only has the 8.0.402 SDK. Can we just try to remove the global.json entirely and go with the default?

[armanossiloko]

Looks like the build failed because GitHub Actions only has the 8.0.402 SDK. Can we just try to remove the global.json entirely and go with the default?

Absolutely. I've removed it now. Let's see how it goes.

[armanossiloko]

Looks like the build is good now, but the SpaFallback tests are failing - guess changing the target framework to net8.0 was enough to break its behavior. :D When I created an MVC app on my own, it worked just fine. lol

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.03%. Comparing base (86ff5dd) to head (c6e9ecb).
Report is 12 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #207      +/-   ##
==========================================
+ Coverage   81.94%   82.03%   +0.09%     
==========================================
  Files          31       31              
  Lines        1102     1102              
  Branches      125      123       -2     
==========================================
+ Hits          903      904       +1     
  Misses        159      159              
+ Partials       40       39       -1     

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[khellang]

Thanks for your awesome contribution, @armanossiloko! 🙏🏻