Add dotnet coverage task

[tevoinea]

Summary of the Pull Request

What is this about?

PR Checklist

• Closes Add dotnet_coverage task #2006
• CLA signed. If not, go over here and sign the CLI.
• Tests added/passed
• Requires documentation to be updated
• I've discussed this with core contributors already. If not checked, I'm ready to accept this work might be rejected in favor of a different grand plan. Issue number where discussion took place: #xxx

Info on Pull Request

What does this include?

Validation Steps Performed

How does someone test & validate?

1. Build a dotnet project
2. Include dll, pdb, and runtimeconfig.json in setup container
3. Add some files in the inputs container
4. Create a new job
5. Create a new task. Example config: onefuzz tasks create 4e43e15a-b003-4d5d-bc37-7907f0a7d527 dotnet_coverage testcoverage.dll coverage=coverage setup=setup readonly_inputs=inputs linux --target_options {input}
6. Verify a cobertura-coverage.xml file is in the coverage container
7. Upload another file in the input container
8. Verify the cobertura-coverage.xml file was updated