docs: add fan-out fan-in section to workflows page (#573)

## 📝 Description

- Add Fan-Out, Fan-In section back from the old docs to the current docs
- Add a Job Matrix video to the job pages

See #572 for more information

Note: waiting for YouTube video to be published

## ✅ Checklist
- [X] I have tested this change
- [ ] This change requires documentation update

Author: TomFern

docs/docs/using-semaphore/img/fan-out-fan-in.jpg

@@ -1089,6 +1089,8 @@ It's not possible to use job parallelism at the same time as [job matrices](#mat
 
 ## Job matrix {#matrix}
 
+<VideoTutorial title="How to use a Job Matrix" src="https://www.youtube.com/embed/jRpj2Pu5eak" />
+
 A job matrix is a more advanced form of [job parallelism](#job-parallelism) where you can define multiple variables with different values and run all the possible permutations.
 
 For example, let's say we want to test our application using three Node.js versions using npm and yarn

docs/docs/using-semaphore/img/fan-out-stage1.jpg

@@ -27,30 +27,159 @@ Before you can run a workflow in Semaphore you need:
 - A Semaphore project linked to the repository
 - One or more pipelines
 
-The [project page](./projects#view-projects) shows all the recent workflows for the project. 
+The [project page](./projects#view-projects) shows all the recent workflows for the project.
 
 ![Types of workflows](./img/workflow-types.jpg)
 
 ## Visual workflow editor {#workflow-editor}
 
 <VideoTutorial title="How to use the workflow builder" src="https://www.youtube.com/embed/dg2jDQmYJ_4" />
 
-You can define most aspects of your workflows using the visual editor. 
+You can define most aspects of your workflows using the visual editor.
 
 To access the editor, open one of your projects on and press **Edit Workflow**. All your changes are stored as YAML pipeline definitions on your Git repository. You can make changes using the visual editor, or edit the YAML directly by clicking on the pipeline YAML file.
 
 ![Workflow editor button](./img/workflow-editor.jpg)
 
 See the [jobs page](./jobs) to learn how to define jobs and blocks.
 
+## Modeling Complex Workflows {#modeling-complex-workflows}
+
+This section provides guides to model complex, non-linear CI/CD processes.
+
+### Fan-out Fan-In {#fan-out-fan-in}
+
+<VideoTutorial title="Fan Out - Fan In" src="https://www.youtube.com/embed/HKv-jMkC7T0" />
+
+The Fan-Out Fan-In workflow provides consistency and maximum parallelization. It can be split into 3 stages:
+
+1. **Build stage**: you build your project once
+2. **Fan-Out stage**: all your tests fan out from the build stage and run in parallel
+3. **Fan-In stage**: once tested, the workflow fans in to a release or deploy stage
+
+![Fan-Out Fan-In](./img/fan-out-fan-in.jpg)
+
+<Tabs groupId="editor-yaml">
+<TabItem value="editor" label="Editor" default>
+
+<Steps>
+
+1. Create your build [job](./jobs). Depending on the nature of your project, you can save the built artifact to the [artifact store](./artifacts) or push it to a [Docker registry](./containers/docker)
+
+      ![Build stage](./img/fan-out-stage1.jpg)
+
+2. Add your test jobs. Set dependencies so all your tests depend on the build job created on Step 1
+
+      ![Fan-out stage](./img/fan-out-stage2.jpg)
+
+3. Add the release/deploy job. Use dependencies so the new job depends on all your tests. This will make the release/job run only if all tests have passed
+
+      ![Fan-in stage](./img/fan-out-stage3.jpg)
+
+</Steps>
+
+</TabItem>
+<TabItem value="yaml" label="YAML">
+
+You can create a Fan-Out Fan-In workflow by setting the dependencies in your blocks. The Fan-Out stage is achieved by defining `dependencies`. For example:
+
+```yaml
+blocks:
+  - name: "Build"
+    dependencies: []
+    ...
+
+  - name: "Unit tests"
+    dependencies: ["Build"]
+    ...
+
+  - name: "Integration tests"
+    dependencies: ["Build"]
+    ...
+
+  - name: "E2E tests"
+    dependencies: ["Build"]
+    ...
+
+  - name: "Release candidate"
+    dependencies: ["Integration tests", "Unit tests", "E2E tests"]
+    ...
+```
+
+Find below a complex example of a Fan-Out, Fan-In for a Node-based workflow:
+
+```yaml
+version: v1.0
+name: Continuous Integration Pipeline
+agent:
+  machine:
+    type: f1-standard-2
+    os_image: ubuntu2204
+blocks:
+  - name: Build Stage
+    dependencies: []
+    task:
+      jobs:
+        - name: Build Project
+          commands:
+            - 'checkout'
+            - 'npm run build'
+            - 'artifact push workflow build/'
+  - name: End to end tests
+    dependencies:
+      - Build Stage
+    task:
+      jobs:
+        - name: Run E2E tests
+          commands:
+            - 'checkout'
+            - 'artifact pull workflow build/'
+            - 'npm run test:e2e'
+  - name: Integration Tests
+    dependencies:
+      - Build Stage
+    task:
+      jobs:
+        - name: Run integration tests
+          commands:
+            - 'checkout'
+            - 'artifact pull workflow build/'
+            - 'npm run test:integration'
+  - name: Unit tests
+    dependencies:
+      - Build Stage
+    task:
+      jobs:
+        - name: Run unit tests
+          commands:
+            - 'checkout'
+            - 'artifact pull workflow build/'
+            - 'npm run test:unit'
+  - name: Release candidate
+    dependencies:
+      - End to end tests
+      - Integration Tests
+      - Unit tests
+    task:
+      jobs:
+        - name: Generate RC
+          commands:
+            - 'checkout'
+            - 'artifact pull workflow build/'
+            - 'npm run package'
+```
+
+</TabItem>
+</Tabs>
+
 ## Workflow triggers
 
 The following events or actions trigger workflows by default:
 
 - Pushing commits into any branch
 - Pushing Git tags
 - Changing any pipelines
-- Manually re-running workflows 
+- Manually re-running workflows
 - Running pipelines using [Tasks](./tasks)
 
 Additionally, you can configure workflows to be triggered by:
@@ -117,12 +246,11 @@ Approving forked pull requests is limited to new comments only and does not work
 
 ## How to skip commits {#skip}
 
-If you don't want to start a workflow, type one of the following strings in the commit message. 
+If you don't want to start a workflow, type one of the following strings in the commit message.
 
 - `[ci skip]`
 - `[skip ci]`
 
-
 For example, this push does not trigger a Semaphore pipeline execution, it is completely ignored:
 
 ```shell title="Skipping a commit"