Docs: Changes heading levels and builds more structure

Updated the doc so it's easier to see which options are available.

doc/ci/docker/using_kaniko.md

@@ -13,7 +13,7 @@ type: howto
 container images from a Dockerfile, inside a container or Kubernetes cluster.
 
 kaniko solves two problems with using the
-[Docker-in-Docker build](using_docker_build.md#use-the-docker-executor-with-the-docker-image-docker-in-docker)
+[Docker-in-Docker build](using_docker_build.md#use-docker-in-docker)
 method:
 
 - Docker-in-Docker requires [privileged mode](https://docs.docker.com/engine/reference/run/#runtime-privilege-and-linux-capabilities)

doc/user/packages/container_registry/index.md

@@ -299,7 +299,7 @@ is set to `always`.
 
 To use your own Docker images for Docker-in-Docker, follow these steps
 in addition to the steps in the
-[Docker-in-Docker](../../../ci/docker/using_docker_build.md#use-the-docker-executor-with-the-docker-image-docker-in-docker) section:
+[Docker-in-Docker](../../../ci/docker/using_docker_build.md#use-docker-in-docker) section:
 
 1. Update the `image` and `service` to point to your registry.
 1. Add a service [alias](../../../ci/services/index.md#available-settings-for-services).
@@ -329,7 +329,7 @@ error during connect: Get http://docker:2376/v1.39/info: dial tcp: lookup docker
 
 To use your own Docker images with Dependency Proxy, follow these steps
 in addition to the steps in the
-[Docker-in-Docker](../../../ci/docker/using_docker_build.md#use-the-docker-executor-with-the-docker-image-docker-in-docker) section:
+[Docker-in-Docker](../../../ci/docker/using_docker_build.md#use-docker-in-docker) section:
 
 1. Update the `image` and `service` to point to your registry.
 1. Add a service [alias](../../../ci/services/index.md#available-settings-for-services).

doc/user/project/merge_requests/browser_performance_testing.md

@@ -63,7 +63,7 @@ on your code by using GitLab CI/CD and [sitespeed.io](https://www.sitespeed.io)
 using Docker-in-Docker.
 
 1. First, set up GitLab Runner with a
-   [Docker-in-Docker build](../../../ci/docker/using_docker_build.md#use-the-docker-executor-with-the-docker-image-docker-in-docker).
+   [Docker-in-Docker build](../../../ci/docker/using_docker_build.md#use-docker-in-docker).
 1. Configure the default Browser Performance Testing CI/CD job as follows in your `.gitlab-ci.yml` file:
 
    ```yaml

doc/user/project/merge_requests/code_quality.md

@@ -67,7 +67,7 @@ the merge request's diff view displays an indicator next to lines with new Code
 
 This example shows how to run Code Quality on your code by using GitLab CI/CD and Docker.
 
-- Using shared runners, the job should be configured For the [Docker-in-Docker workflow](../../../ci/docker/using_docker_build.md#use-the-docker-executor-with-the-docker-image-docker-in-docker).
+- Using shared runners, the job should be configured For the [Docker-in-Docker workflow](../../../ci/docker/using_docker_build.md#use-docker-in-docker).
 - Using private runners, there is an [alternative configuration](#set-up-a-private-runner-for-code-quality-without-docker-in-docker) recommended for running Code Quality analysis more efficiently.
 
 In either configuration, the runner must have enough disk space to handle generated Code Quality files. For example on the [GitLab project](https://gitlab.com/gitlab-org/gitlab) the files are approximately 7 GB.
@@ -226,7 +226,7 @@ are configured with `privileged=true`, and they do not expose `docker.sock` into
 the job container. As a result, socket binding cannot be used to make `docker` available
 in the context of the job script.
 
-[Docker-in-Docker](../../../ci/docker/using_docker_build.md#use-the-docker-executor-with-the-docker-image-docker-in-docker)
+[Docker-in-Docker](../../../ci/docker/using_docker_build.md#use-docker-in-docker)
 was chosen as an operational decision by the runner team, instead of exposing `docker.sock`.
 
 ### Disabling the code quality job

doc/user/project/merge_requests/load_performance_testing.md

@@ -103,7 +103,7 @@ job.
 An example configuration workflow:
 
 1. Set up GitLab Runner to run Docker containers, like the
-   [Docker-in-Docker workflow](../../../ci/docker/using_docker_build.md#use-the-docker-executor-with-the-docker-image-docker-in-docker).
+   [Docker-in-Docker workflow](../../../ci/docker/using_docker_build.md#use-docker-in-docker).
 1. Configure the default Load Performance Testing CI/CD job in your `.gitlab-ci.yml` file.
    You need to include the template and configure it with CI/CD variables: