We perform lookups on sidebar section links based on sidebar_section_id
totally ignoring user. This ensures we have an index to work with.
This removes the previous index `links_user_id_section_id_position` which
partially doubled up `idx_unique_sidebar_section_links`
Allows users to configure their own custom sidebar sections with links withing Discourse instance. Links can be passed as relative path, for example "/tags" or full URL.
Only path is saved in DB, so when Discourse domain is changed, links will be still valid.
Feature is hidden behind SiteSetting.enable_custom_sidebar_sections. This hidden setting determines the group which members have access to this new feature.
Krzysztof Kotlarek
Sam
David Taylor
Alan Guo Xiang Tan