Add Starred Snippets

Description

A snippet was recommended to me, however there is no way mark it as "starred" so that I can more easily find it later.

We currently have Starred projects, which makes it easy to star a project you're interested in and be able to find it later.

But we don't have a "Starred snippets", just this

Proposal

Add a way to "star" a snippet, like we can do for projects, and be able to list them.

Testing Activity

@lulalala:

• Test starring works for both web and API calls Star creation/deletion

@vij:

• Snippet visibility level change impacts
• Test dependency changes (Snippet deletion, Project deletion/snippets disabled/etc)
• Test Finder with starred snippets / no starred snippets / visibility levels (project scoping)

@a_luna:

• Starring a snippet creates an association between the snippet and the user
• Unstarring a snippet deletes the association between the snippet and the user
• If a snippet is already starred there shouldn’t be any duplicates created

Security Testing

• Test starred snippet access for other users (@vij)

MR Breakdown

@lulalala:

• 1 MR (db)
• 1 MR (controller)
• 1 MR (API)

@vij:

• 1 MR for basic starring support (relationships, actions, refactor of starred projects common functionality)
• 1 MR for starred snippets UI support (finders, counts)
• 1 MR for API / GraphQL support if required

@a_luna:

• 1 MR adding the association between starred snippets and user (with a new table)
• 1 MR adding endpoint to star/unstar snippets
• 1 MR adding methods to list starred snippets for the user
• 1 MR with FE changes
• 1 MR for API changes

Links / references

https://gitlab.com/gitlab-org/gitlab-ce/issues/19336