What this PR does / why we need it:

Renaming labels using label_format dst=src is broken on main. Destination label does not appear in the resulting label set if the source is a stream label. This is because we don't append the labels from add[StreamLabel] list to the resulting buffer, this looks like a conscious choice to not pollute StreamLabels.

I felt the correct fix here is to correctly tag the renamed label as a ParsedLabel. This also makes sure the new label supersedes any structured metadata if present.

Which issue(s) this PR fixes:
Fixes #

Special notes for your reviewer:

Checklist

• Reviewed the CONTRIBUTING.md guide (required)
• Documentation added
• Tests updated
• Title matches the required conventional commits format, see here
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