approval-distribution: Add approvals/assignments spans on all paths (#7317)

* approval-distribution: Add approvals/assignments spans on all paths

The approval and assignment logic gets called from multiple paths, so make sure
we create a tracing span on all paths to make debugging easier and be able and
correlate with the spans from approval-voting.

Signed-off-by: Alexandru Gheorghe <[email protected]>

* Tag each label with a difference tracing name

Signed-off-by: Alexandru Gheorghe <[email protected]>

* Address review feedback

Use the source to determine the tag name

Signed-off-by: Alexandru Gheorghe <[email protected]>

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Signed-off-by: Alexandru Gheorghe <[email protected]>