Docs: loki.md: Add example of Loki data source config (#29976)
Docs: loki.md: Add example of Loki data source config (#29976)

* loki.md: Add example of Loki data source config

It was little difficult to search an example of setting datasourceUid for Jaeger data source. 

I found the answer from https://github.com/grafana/grafana/issues/26087 and thought it would be good to document it.

* Update docs/sources/datasources/loki.md

Co-authored-by: Diana Payton <ee24b2c2426ceb8f7f9d3f1e01be1306fa31b8a1@users.noreply.github.com>

* Update docs/sources/datasources/loki.md

Co-authored-by: Diana Payton <ee24b2c2426ceb8f7f9d3f1e01be1306fa31b8a1@users.noreply.github.com>

Co-authored-by: Diana Payton <ee24b2c2426ceb8f7f9d3f1e01be1306fa31b8a1@users.noreply.github.com>
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