Change urgency of API project/:id/share to `low`

What does this MR do and why?

Backports !166396 (merged).

Change urgency of API project/:id/share to low

This endpoint does not meet the default latency target of 1 second in some scenarios. So changing the urgency to low instead. 5 second target should be tolerable for this endpoint.

Related: #489465 (closed)

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