Adds `#build_notification_recipients` to `NotificationRecipientService`
that returns the `NotificationRecipient` objects in order to be able to
access the new attribute `reason`.

This new attribute is used in the different notifier methods in order to
add the reason as a header: `X-GitLab-NotificationReason`.

Only the reason with the most priority gets sent.

Closes https://gitlab.com/gitlab-com/gitlab-docs/issues/142

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

delete old doc, update links to the current doc

- correct the file tree
- remove duplicate doc
- move to project/members/
- move images
- update links

fix the file tree

Update gitlab_flow.md, Teatro seems to be completely dead, see also https://forum.gitlab.com/t/gitlab-flow-documentation-teatro/7774

other than just removing a key, which doesn't affect the verified state
of a commit, revoking a key unverifies all signed commits.

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`

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

Notification settings are described, but aren't mentioned where they
are or where to change them.

- Move to dicsussions/index.md
- Bring back previous path with a link to new location
- Reorder sections

Enables user specification of group name vs. name inferred from group path.

Cause new group form to copy name from path

Adds some new page-specific javascript that copies entry from the
group path field to the group name field when the group name field
is initially empty.

Remove duplicate group name entry field on group edit form

This corrects the duplicated name entry field and tests that the
JavaScript does not update the group name field if the user
edits the group path.  (Editing the group path is not recommended
in any case, but it is possible.)

Address eslint errors in group.js

Enable group name copy with dispatch and explore group creation

The dispatch and explore group creation forms require the group.js
asset, and their tests now require testing against poltergeist

Update workflow new group instruction

Update the gitlab basics group creation document

Add a change log entry

Remove unused variable for eslint