Wrapper method to easily retry deadlock exceptions

[juliusknorr]

Wrapper around atomic() to retry after a retryable exception occurred

Certain transactions might need to be retried. This is especially useful in highly concurrent requests where a deadlocks is thrown by the database without waiting for the lock to be freed (e.g. due to MySQL/MariaDB deadlock detection)

[szaimen]

CI failure unrelated

[DaphneMuller]

Hello!
Thank you for your work on this! I noticed that your PR still has the label 'documentation'. I'm not sure if you already had a look at the documentation for your PR, but at Nextcloud we strive to document changes that affect other app developers or other admins before the release takes place, and I'm pinging you with the hope to get this done.

Are you familiar with our documentation process already?
Changes that affect app developers should be documented here:
https://docs.nextcloud.com/server/27/developer_manual/app_publishing_maintenance/app_upgrade_guide/upgrade_to_27.html

Changes that affect administrators should be documented here:
https://docs.nextcloud.com/server/latest/admin_manual/release_notes/upgrade_to_27.html

While I understand sometimes it's handy to merge fast to get your changes in, it would be great if next time you could try to add the documentation before merging. You can find more information on that here:
https://docs.nextcloud.com/server/27/developer_manual/prologue/compatibility_app_ecosystem.html#documentation-procedures-of-changes-that-affect-app-developers

If all your documentation efforts are done, please remove the label 'documentation' and check the checkbox in your opening note and I'll stop bugging you :)

Many thanks in advance and thanks again for your work!

[juliusknorr]

Started as nextcloud/documentation#10514 but will extend that a bit with more details later