Workhorse was not able to parse the `headers` property since it was expecting a
key => array as a structure.

Error from workhorse: preAuthorizeHandler: decode authorization response: json:
cannot unmarshal string into Go struct field TerminalSettings.Header of type
[]string

Workhorse was not changed since this api is already used for the environment
terminals.

gitlab-org/gitlab-ce#25990

Update doc/ci/docker/using_docker_build.md

Closes #48691

See merge request gitlab-org/gitlab-ce!20426

Add example output for file integrity check rake task

Closes #49244

See merge request gitlab-org/gitlab-ce!20825

Fix: redirect non-SSL request for gitlab registry to valid URL

See merge request gitlab-org/gitlab-ce!20824

HTTP host and URI should not be separated by a colon. Generated URLs was looking like http://registry.examples.com:/foo. That is throwing up let's encrypt cert requests for gitlab registry.

Fix slow Markdown rendering

Closes #49409

See merge request gitlab-org/gitlab-ce!20820

The sanitize transformers were being duplicated each time the Markdown
renderer was called, leading to expontential growth in rendering times.

The problem was that although HTML::Pipeline::SanitizationFilter.WHITELIST
is a frozen hash, the `:transformers` array can be modified. We need
to do deep copy of this to avoid adding duplicates.

Closes #49409

Add best practice points regarding background migrations on huge tables

See merge request gitlab-org/gitlab-ce!20815