worker: make some parameters configurable

Created by: asdine

This adds some very conservative defaults for the Bitbucket Project Permissions worker. Because we had some deadlock issues, we are making the default concurrency to 1 and let the user increase the value as needed. In case of deadlock, one of the job will win and the other will retry after 30s. The default retry interval has been set to 30s to avoid sending too many requests to Bitbucket. Some parameters have been ignored as they are also ignored in other worker implementations.

Test plan

Unit tests