Increasing coverage and simplifying coverage report creation.

[davidadas]

This has no breaking changes or customer facing features.

Checklist

• [x] I have successfully built and used a custom CLI binary, without linter issues from this PR.
• [x] I have clearly specified in the What section below whether this PR applies to Confluent Cloud, Confluent Platform, or both.
• [x] I have verified this PR in Confluent Cloud pre-prod or production environment, if applicable.
• [x] I have verified this PR in Confluent Platform on-premises environment, if applicable.
• [x] I have attached manual CLI verification results or screenshots in the Test & Review section below.
• [x] I have added appropriate CLI integration or unit tests for any new or updated commands and functionality.
• [x] I confirm that this PR introduces no breaking changes or backward compatibility issues.
• [x] I have indicated the potential customer impact if something goes wrong in the Blast Radius section below.
• [x] I have put checkmarks below confirming that the feature associated with this PR is enabled in:
  • [x] Confluent Cloud prod
  • [x] Confluent Cloud stag
  • [x] Confluent Platform
  • [x] Check this box if the feature is enabled for certain organizations only

What

• Increased coverage of various unit and integration tests.
• Set gotestsum runs both in the Semaphore pipeline and locally.
• Amended the .gitignore to include other coverage artifacts.

Blast Radius

The blast radius here is nil. At worst, it will cause unit or integ tests to fail or for the coverage to run improperly.

References

N/A

Test & Review

It is tests, so it has indeed been tested.

[confluent-cla-assistant[bot]]

:tada: All Contributor License Agreements have been signed. Ready to merge.
:white_check_mark: davidadas
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