feat: rework CI pipeline to support C# 12, .NET 8.0 and tests on .NET Framework 4.8

[Sylvain2703]

Proposed Changes

Features

• Complete rework of the CI pipeline to build with the latest .NET SDK and support C# 12:
  • The .NET solution is now built and packed only once, with a .NET 8 SDK Docker image,
  • The resulting build is copied for testing with .NET Core 3.1/5/6/7/8 Docker images (thanks to CircleCI workspaces),
  • Install and onboard InfluxDB 2.x to perform all tests on Windows (previously only Client.Legacy was tested),
  • The tested build is used for deployment (instead of rebuilding it),
  • Make code coverage work again (seems broken since 8038ed21, as its parent commit is the last one published on Codecov).
• Add support for .NET 8.0 and .NET Framework 4.8 on test projects.

Tests

• Adjust tests to pass on Windows.

Build

• Move ExampleConsole project into a subfolder to avoid it being in the same folder as ExampleBlazor.
• Remove warnings for out of support target frameworks in test and example projects.

Checklist

• [ ] CHANGELOG.md updated
• [x] Rebased/mergeable
• [x] A test has been added if appropriate
• [x] dotnet test completes successfully
• [x] Commit messages are conventional
• [x] Sign CLA (if not already signed)

[codecov-commenter]

Codecov Report

Attention: 10 lines in your changes are missing coverage. Please review.

Comparison is base (9c54998) 87.13% compared to head (5d97ebf) 89.26%. Report is 87 commits behind head on master.

Files	Patch %	Lines
Client.Core/Internal/AbstractQueryClient.cs	60.00%	3 Missing and 1 partial :warning:
Client.Core/Internal/EnumConverter.cs	0.00%	2 Missing :warning:
Client/Internal/ApiClient.cs	83.33%	2 Missing :warning:
Client/Internal/MeasurementMapper.cs	0.00%	2 Missing :warning:

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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #613      +/-   ##
==========================================
+ Coverage   87.13%   89.26%   +2.12%     
==========================================
  Files          77       47      -30     
  Lines        6893     2123    -4770     
  Branches        0      311     +311     
==========================================
- Hits         6006     1895    -4111     
+ Misses        887      176     -711     
- Partials        0       52      +52     

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