fix: remove empty session_id values from aggregated count

[daibhin]

Problem

We see a ton of issues with large occurrence / user counts but the session count is 1 🤔

We thought this was because NULL was being counted as a distinct value but CH docs confirm that NULL values are excluded from the count. Upon investigation it seems like the $session_id can sometimes be a blank string, which is a distinct value we want to exclude

Changes

• Exclude empty string $session_id by casting them to NULL
• Handle things nicely on the frontend with tooltips to explain what is going on

[github-actions]

Size Change: 0 B

Total Size: 1.13 MB

ℹ️ View Unchanged

Filename	Size
frontend/dist/toolbar.js	1.13 MB

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