Add more no-stage metadata to pages

Mark these pages as not belonging to any particular stage.

doc/development/documentation/workflow.md

+---
+stage: none
+group: unassigned
+info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#designated-technical-writers
+---
+
 # Documentation process
 
 The process for creating and maintaining GitLab product documentation allows

doc/development/go_guide/index.md

+---
+stage: none
+group: unassigned
+info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#designated-technical-writers
+---
+
 # Go standards and style guidelines
 
 This document describes various guidelines and best practices for GitLab

doc/development/shell_scripting_guide/index.md

+---
+stage: none
+group: unassigned
+info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#designated-technical-writers
+---
+
 # Shell scripting standards and style guidelines
 
 GitLab consists of many various services and sub-projects. The majority of

doc/development/testing_guide/testing_migrations_guide.md

 ---
+stage: none
+group: unassigned
+info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#designated-technical-writers
 type: reference
 ---
 

doc/topics/autodevops/customize.md

+---
+stage: none
+group: unassigned
+info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#designated-technical-writers
+---
+
 # Customizing Auto DevOps
 
 While [Auto DevOps](index.md) provides great defaults to get you started, you can customize