Fix for update 8.10-to-8.11.md doc.

## What does this MR do?

Fixed a typo in the docs to update Ruby.

See merge request !5941

Bump SimpleCov merge timeout to 365 days

## What does this MR do?

In case that CI pipeline fails because of intermittent errors in one of the jobs, when someone retries the only failing job located in the middle stage, the job that calculates compound coverage that is configured in later stage, and triggered after retrying job in the pipeline, will still return an accurate coverage value.

Closes #21144

See merge request !5932

Add Ruby 2.3 upgrade notes.

The 8.10 to 8.11 docs didn't mention Ruby 2.3, now they do.

See merge request !5940

Split Koding admin/user docs

Backend/Frontend MR https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/5909

See merge request !5938

Documentation for Issue Boards

## What does this MR do?

Add documentation for issue boards.

## What are the relevant issue numbers?

- Issue: https://gitlab.com/gitlab-org/gitlab-ce/issues/17907
- Backend MR: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/5548
- Frontend MR: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/5554

See merge request !5713

Change slash commands docs location



See merge request !5937

Fix typo in gitlab-workhorse header

See merge request !5891

Document protected branches new behavior



See merge request !5934

Fix empty dropdown

Deselecting the current selected option on a dropdown they were removing the input related to them.
This led to a unexpected cases. The forms were submitted without all required inputs and the label was still indicating an option was selected. This MR fixes that.

See merge request !5927

Before this the dropdowns were not being disabled if the user unselected an option from the allowed to merge/push dropdowns.

No need to update the branch permission if no option is marked on the dropdown

This makes dropdown to look according the dropdowns on the edit form. This options add a tick mark next to the selected option.

Fix inputs not being found due to incorrect class in wrap element

Fixes failing spec

See merge request !5926