TodoService should not call `.select(&:id)` on todos, because this is
bad performance. So instead use sub-queries, which will result in a
single SQL query to the database.

https://docs.gitlab.com/ee/development/sql.html#plucking-ids

Added the ability to 'Undo mark all as done' todos marked as complete with 'Mark all as done'
in the 'Todo' tab of the Todo dashboard.
The operation undos only the todo previously marked as done with the 'Mark al as done' button.

 Rename column in the database
 Rename fields related to import/export feature
 Rename API endpoints
 Rename documentation links
 Rename the rest of occurrences in the code
 Replace the images that contain the words "build succeeds" and docs referencing to them
 Make sure pipeline is green and nothing is missing.

updated doc images

renamed only_allow_merge_if_build_succeeds in projects and fixed references

more updates

fix some spec failures

fix rubocop offences

fix v3 api spec

fix MR  specs

fixed issues with partials

fix MR spec

fix alignment

add missing v3 to v4 doc

wip - refactor v3 endpoints

fix specs

fix a few typos

fix project specs

copy entities fully to V3

fix  entity error

more fixes

fix failing specs

fixed missing entities in V3 API

remove comment

updated code based on feedback

typo

fix spec

The Done button will change to an Undo button and the line item will be greyed out.
Bold links will be unbolded.
The user can undo the task by clicking the Undo button.

on the UI when mark as done a already done todo.

Follow-up on 52b0c26

Signed-off-by: NRémy Coutable <remy@rymai.me>

We’re being kept up to date the counter data but we’re not using it.
The only thing which is not real if is the number of projects that the 
user read changes the number of todos can be stale for some time.

The counters will be sync just after the user receives a new todo or mark any as done

- As todos are created/updated inside the TodoService
we repopulate the cache just there for both pending/done todos
- Todos as mark as done from the TodosController we update cache
there too
- All the added methods are kept in the User class for cohesion

This reverts commit 13e37a3e.

Added a button into the sidebar for issues & merge requests to allow users to manually create todo items

Closes #15045

This reverts commit 3e991230.

# Conflicts:
#	app/models/project.rb

When a build fails for a commit, create a todo for the author of the
merge request that commit is the HEAD of. If the commit isn't the HEAD
commit of any MR, don't do anything. If there already is a todo for that
user and MR, don't do anything.

Current limitations:
- This isn't configurable by project.
- The author of a merge request might not be the person who pushed the
  breaking commit.

Signed-off-by: NRémy Coutable <remy@rymai.me>

Since potentially the previous assign-task has already been handled.