feat: OTEL support is missing docs

[hdrebin]

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Problem Description

OTEL support was allegedly introduced in v 0.60 (https://github.com/open-webui/open-webui/releases/tag/v0.6.0), which is great, but there is no further docs on how to use this, and it says that it is opt-in, so I am sort of missing some more info in order to get this up and running. Should be a quick win? :)

Desired Solution you'd like

Added docs on how to configure

Alternatives Considered

No response

Additional Context

No response