Implement allowing child pipeline to have child pipeline

See merge request gitlab-org/gitlab!41102

In this commit, we are just allowing parent->child->child nesting.
This is controlled by MAX_DESCENDANTS_DEPTH constant.

This feature is also behind a FF ci_child_of_child_pipeline for now.

Upgrade GitLab Pages to 1.24.0

See merge request gitlab-org/gitlab!41782

Remove expired_pat_email_notification feature flag

See merge request gitlab-org/gitlab!41166

Feature flag rollout `search_track_unique_users`

See merge request gitlab-org/gitlab!41739

Update log_tree to use immutable cache update

See merge request gitlab-org/gitlab!41746

- graphql config
- log_tree update
- test adjustments

Update Gitaly version

See merge request gitlab-org/gitlab!41322

Internationalize Admin users new

See merge request gitlab-org/gitlab!41367

Remove feature flag buy_ci_minutes_version_a_experiment_percentage

See merge request gitlab-org/gitlab!41632

Internationalize Admin namespace plan

See merge request gitlab-org/gitlab!41363

Formatted markdown tables for Geo datatypes

See merge request gitlab-org/gitlab!41736

Added the main reasons for beta status of object storage replication

See merge request gitlab-org/gitlab!41314

Externalize i18n strings from app/views/shared/snippets/_header.html.haml

See merge request gitlab-org/gitlab!41235

Externalize i18n strings from app/views/shared/runners/show.html.haml

See merge request gitlab-org/gitlab!41241

Store package creator

See merge request gitlab-org/gitlab!41258

Update the link for "Is it any good?" section

See merge request gitlab-org/gitlab!41729

Remove designs from incidents

Closes #244947

See merge request gitlab-org/gitlab!41757

Docs: clarify File Locking workflow

See merge request gitlab-org/gitlab!40972

Add update issue by id mutation

See merge request gitlab-org/gitlab!41226

The flag was introduced in 13.3 and has been stable
for a release.

Update description when editing iteration

See merge request gitlab-org/gitlab!40476

[RUN AS-IF-FOSS] Place packages scope under Package Registry condition

See merge request gitlab-org/gitlab!35334

Only display the settings for the packages scope when the packages
features is enabled in the group or project.

Fix a typo in WikiPages::UpdateService messaging

See merge request gitlab-org/gitlab!41776

Minor bottom spacing add to align with top spacing

See merge request gitlab-org/gitlab!41596

Merge branch '33895-expand-supported-number-projects-on-environments-dashboard-by-adding-pagination-2' into 'master'

Document adding an application limit to Environment Dashboard

See merge request gitlab-org/gitlab!40703

Export audit events to CSV

See merge request gitlab-org/gitlab!31191

New Crowdin translations - 04 September 2020

See merge request gitlab-org/gitlab!41615

[skip ci]

Add note to graphql timelog_type

Closes #231284

See merge request gitlab-org/gitlab!37748

Display affected test files in detect-tests jobs

See merge request gitlab-org/gitlab!41719

Resolve failure in configure_issue_board_by_label_spec

Closes #245182

See merge request gitlab-org/gitlab!41540