Update Bitbucket Cloud Importer to map users by uuid

What does this MR do and why?

This MR updates Bitbucket Cloud importer to map user contributions by Bitbucket user's uuid instead of a nickname. We previously updated bitbucket oauth strategy to create a user identity for bitbucket provider to use uuid instead of a username. This made bibucket importer stop mapping user contributions. This MR fixes this issue.

Mentions #461562 (closed)

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Import where user can be mapped	Import where user cannot be mapped

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