feat: create periodic replay embedding task

[daibhin]

Problem

We want to generate embeddings on a periodic schedule

Changes

This sets up one task which runs every five minutes (configurably)
That task returns a list of recordings, each recording is pushed onto a separate celery queue for embedding

The code that does this work is in #20046
and that will internally handle not trying to process too many at a time and measuring what is run so we can tune it

[github-actions]

Size Change: 0 B

Total Size: 2.22 MB

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frontend/dist/toolbar.js	2.22 MB

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[pauldambra]

I'm going to merge this into the other PR so there's just one PR - the two aren't quite lining up and it'll be easier in one

[pauldambra]

merged this into #20046