What is the problem?
When an admin changes the default_sidebar_categories or default_sidebar_tags site settings and opts to backfill the setting,
we currently enqueue a sidekiq job to run the backfilling operation. When an admin changes those settings multiple times
within a short time frame, multiple sidekiq jobs with different backfilling parameters will be enqueued.
This is problematic if multiple jobs are executed concurrently as it may lead to situations where a job
with “outdated” site setting values is completed after a job with the “latest” site setting values.
What is the fix?
By setting `cluster_concurrency` to `1`, we ensure that only one of such
backfilling job will execute across all the sidekiq processes that are
deployed at any point in time. Since Sidekiq pops off job in the order
in which they are pushed, limiting the cluster concurrency here will
allow us to execute the enqueued `Jobs::BackfillSidebarSiteSettings`
jobs serially.
The previous sidebar default tags and categories implementation did not
allow for a user to configure their sidebar to have no categories or
tags. This commit changes how the defaults are applied. When a user is being created,
we create the SidebarSectionLink records based on the `default_sidebar_categories` and
`default_sidebar_tags` site settings. SidebarSectionLink records are
only created for categories and tags which the user has visibility on at
the point of user creation.
With this change, we're also adding the ability for admins to apply
changes to the `default_sidebar_categories` and `default_sidebar_tags`
site settings historically when changing their site setting. When a new
category/tag has been added to the default, the new category/tag will be
added to the sidebar for all users if the admin elects to apply the changes historically.
Like wise when a tag/category is removed, the tag/category will be
removed from the sidebar for all users if the admin elects to apply the
changes historically.
Internal Ref: /t/73500
