Fragile JSON manipulation via sed in gstack-telemetry-sync

[robertoecf]

Found during review.

File: bin/gstack-telemetry-sync:85

Using `sed` with regex to strip fields from JSON is fragile — breaks if values contain commas, escaped quotes, or if field order changes. Since the script already runs in an environment with `jq` (or could use bun), this would be more reliable:

CLEAN=\$(echo "\$LINE" | jq -c 'del(._repo_slug, ._branch, .repo)')

Not urgent but avoids silent data corruption in the telemetry pipeline.