Update to add all issues to be updated.
 Added functionality, proper tests, documentation and changelog.

Currently, when a user wants to assign an issue/MR to himself, he needs
to type his full username or select it from the suggested ones in the
dropdown list.
This commits suggest a faster solution which is typing `/assign me`

Closes #35304.

- Updated DSL to support substitution definitions
- Added substitution definition, inherits from command definition
- Added tabelflip and shrug substitutions to interpret service
- Added support for substitution definitions to the extractor for preview mode.
- Added substitution handling in the interpret service

Signed-off-by: Alex Ives <alex@ives.mn>

/reassign should only work when multiple assignees are available. And
since this is only the case for GitLab EE, remove it from CE.

This was picked using 517c97eb of gitlab-ee.

Set the assignee to last user in the array if multiple assignees aren't
allowed.

Also, use `parse_params` where possible.

To make it simpler to assign users to an Issuable, make MergeRequest
support the attribute `assignee_ids`.

The /reassign quick command works even when no multiple assignees are allowed of
there isn't any assignee yet. So for consistency, it's also be backported to
CE. But it functions the same as the /assign quick action.

Avoid conflicts when merge CE to EE by backporting code from EE.

Instead of checking in `SlashCommands::InterpretService` what the issuable the
type of the issuable is, ask the issuable if it is capable to do those thing and
implement it in the issuable itself. The issuable will check if it's possible
and if the licensed feature is available.

This should also make it easier to ever add multiple assignees to MergeRequests.

Fix https://gitlab.com/gitlab-org/gitlab-ce/issues/27070

Deprecate "chat commands" in favor of "slash commands"

We looked for things like:

 - `slash commmand`
 - `slash_command`
 - `slash-command`
 - `SlashCommand`

Remove slash commands from Markdown preview and display their outcome next to
the text field.
Introduce new "explanation" block to our slash commands DSL.
Introduce optional "parse_params" block to slash commands DSL that allows to
process a parameter before it is passed to "explanation" or "command" blocks.
Pass path for previewing Markdown as "data" attribute instead of setting
a variable on "window".

 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

add /award slash command; Allow posting of just an emoji in comment

Allows to use slash command /target_branch <target_branch_name> in merge requests notes and description.
Command allows to specify target branch for current merge request.

Proposed in #23619

New endpoints are:

POST :project_id/(issues|merge_requests)/(:issue_id|:merge_request_id)/time_estimate"

POST :project_id/(issues|merge_requests)/(:issue_id|:merge_request_id)/reset_time_estimate"

POST :project_id/(issues|merge_requests)/(:issue_id|:merge_request_id)/add_spent_time"

POST :project_id/(issues|merge_requests)/(:issue_id|:merge_request_id)/reset_spent_time"

GET  :project_id/(issues|merge_requests)/(:issue_id|:merge_request_id)/time_stats"

It toggles the 'WIP' prefix in the MR title.

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