Single commit squash of all changes for https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/10878

It's needed due to https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/10777 being merged with squash.

Fix https://gitlab.com/gitlab-org/gitlab-ce/issues/31271

When the dropdown items are too wide, constrain the dropdown to the
offsetParent. Otherwise, let it naturally flow as Select2 wants.

Fix
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/10602#note_27871752

Fix https://gitlab.com/gitlab-org/gitlab-ce/issues/30637

Closes #31095

This table shows the percentage of users who registered in the last
twelve months, who last signed in during or later than each of those
twelve months, by month.

It is only enabled when the usage ping is enabled, and the page also
shows pretty-printed usage ping data.

The cohorts table is generated in Ruby from some basic SQL queries,
because performing the gap-filling and running sums needed in both MySQL
and Postgres is painful.

CE port of https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/735

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

desired decimals for the cpu metrics

Cleaned up some code

See
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/9461#note_25288831