Deprecation message for dynamic milestone pages

• Deprecation message/graphic for dynamic milestone pages to indicate that we will remove them in a future release.
• In the message/graphic, include some instructions on how to click to one of the project milestones and click Promote so that they can promote their project milestone into a group milestone.
• More context here: https://gitlab.com/gitlab-org/gitlab-ce/issues/39545.
• There are two dynamic milestone pages:
  • Group level: E.g. https://gitlab.com/groups/gitlab-org/-/milestones/100?title=10.0
  • Dashboard level: E.g. https://gitlab.com/dashboard/milestones/95?title=9.5

Design

Copy in the banner

This page will be removed in a future release. 
Use group milestones to manage issues from multiple projects in the same milestone. 
<a href="inline-dropdown">Promote these project milestones into a group milestone.</a>`

• The Learn more button link goes to a docs page explaining the whole context, including the warning of not having burndown charts for group milestones yet, and linking to the open issue for it. It also contains other limitations of group milestones and those open issues.
• Clicking Promote these project milestones into a group milestone, and then dropdown (popover) shows up.

Copy in the popover

1. Click any <b>project name</b> in the project list below to navigate to the project milestone.
2. Click the <b>Promote</b> button in the top right corner to promote it to a group milestone.
<a>Learn more</a>

• The Learn more link : [path-to-docs-ce-or-ee]/user/project/milestones/#promoting-project-milestones-to-group-milestones
• Icons: You can find them in gitlab-svgs.

01	02 - Popover

SVG

You can find milestone_removing-page in gitlab-svgs.