Investigate Codecov support for the GitHub Actions CI loop

[lukebakken]

Discussed in https://github.com/rabbitmq/rabbitmq-dotnet-client/discussions/1529

^{Originally posted by **stebet** April 3, 2024} Since [Codecov](https://codecov.io) is free to use for Open Source Software it would be good to see if it makes sense to add that to the GitHub actions CI loops so we have better visibility into the Code Coverage of the integration tests for example, and to highlight areas for improvement. As long as the licenses are compatible from a legal perspective of course. Is this something you have looked at @lukebakken or @michaelklishin?

[lukebakken]

• https://docs.codecov.com/docs/quick-start
• https://learn.microsoft.com/en-us/dotnet/core/testing/unit-testing-code-coverage?tabs=windows
• https://stackoverflow.com/questions/67911653/how-to-upload-xunit-coverage-reports-to-codecov