Add notice about offline migrations

/cc @sytses 

See merge request !1723

[ci skip]

Use gitlab-workhorse 0.6.4

This fixes a bug in 8.5.0.rc1 where downloading Git blobs through the API is broken.

See merge request !2794

Needed because of !2782.

[ci skip]

[ci skip]

API: Allow to set or update a merge-request's milestone

_Originally opened at !2107 by @ skakirill._

- - -


See merge request !2755

Add a new image in the markdown help page

Previously we were linking directly from the public/
directory. While this worked for the GitLab help page,
it was not working for doc.gitlab.com. Adding an image
in a relative directory and linking from there serves
both ends.

Fixes #13233

See merge request !2790

Previously we were linking directly from the public/
directory. While this worked for the GitLab help page,
it was not working for doc.gitlab.com. Adding an image
in a relative directory and linking from there serves
both ends.

[ci skip]

Fixed "Docker Fundamentals" link in GitLab Documentation.

I noticed that the *Docker Fundamentals* link in the *Using Docker Images* part of the GitLab Documentation is broken.

Screenshot:
![broken-link](/uploads/8d2fc782b2f5d4f3316a631f801cd3c7/broken-link.png)

Changing it to "https://docs.docker.com/" should fix the problem.

See merge request !2786