Check license for milestones on issue boards

Closes #2568

See merge request !2315

Introduce namespace license checks for Push Rules (EES)

Closes #2573

See merge request !2335

Clarify when Code Quality shows in MR widget

Closes #2782

See merge request !2298

Namespace license checks Issue & MR template

Closes #2580

See merge request !2321

And separate EE/CE for board.rb

Introduce namespace license checks for merge request approvers (EES)

Closes #2566

See merge request !2324

# Conflicts:
#   app/models/license.rb

Hide Focus mode button if feature not available in license

Closes #2569

See merge request !2303

Namespace license checks for Contribution Analytics (EES)

Closes #2579

See merge request !2302

Fix EE conflicts for "Allow unauthenticated access to the `/api/v4/users` API"

See merge request !2247

When the Issuable Default Template feature is not available, do not
show the input form to configure the Issue & MR templates on the
Settings page.

Only when the Issuable Default Templates feature is available, fill in
the description from settings when building a new MR.

Only when the license allows Issuable Default Templates, set the issue
description when building an Issue.

Do this by splitting out EE-specific features into
EE::Issues::BuildService. And also split up spec files.

[ci skip]

[ci skip]

Add more logging to repository mirror feature

See merge request !2292

CE Upstream - Monday

See merge request !2325

Add overview and use-cases for Issue Boards EE-only features

See merge request !2296

Move some EE-only KubernetesService code to a prepended module

Closes #2525

See merge request !2168

resolve `spec/helpers/groups_helper_spec.rb`

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>