feat: warn when messages were dropped

[pauldambra]

We now record custom events within a recording when we have to drop messages because they were too large for Kafka

So we can show an error to folk when they view the recordings

(in this view we report 0 dropped messages but that's only so i could get the screenshot, really we don't show it if there are 0)

[github-actions[bot]]

Size Change: 0 B

Total Size: 1.06 MB

ℹ️ View Unchanged

| Filename | Size | | :--- | :---: | | `frontend/dist/toolbar.js` | 1.06 MB |

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