Support Bundle concat code should be consistent with Preflight concat code

[diamonwiggins]

Describe the rationale for the suggested feature.

A recent bug was discovered in the concat code of Preflight - #998. Although there isn't a known issue in the support bundle code, we should update it for consistency.

https://github.com/replicatedhq/troubleshoot/blob/main/pkg/supportbundle/supportbundle.go#L237
https://github.com/replicatedhq/troubleshoot/blob/main/cmd/troubleshoot/cli/run.go#L101-L105

Describe the feature
Refactor the Support Bundle Concat logic to be consistent with the changes in #998

Describe alternatives you've considered

Describe alternative solutions here. Include any workarounds you've considered.

Additional context

Add additional context about the feature request. If the change is substantial, consider attaching files to the issue outlining architectural changes, data flows, file formats etc., anything that helps describe the requested change.

[yangmeilly]

this issue has been annihilated by #1002

[xavpaice]

#933 should resolve this as various parts of the codebase are consolidated. The main issue here is about duplicating the concat code between both preflight and support-bundle, but that duplication sits in many places in the codebase.

I'll close this since we have #1002 handling the specific issue, and #933 to tidy up in general.