docs: add mermaid diagrams

### What does this PR do?

Adds mermaid diagrams to be used within the website.

### Screenshot/screencast of this PR

<!-- Please include a screenshot or a screencast
explaining what is doing this PR -->

### What issues does this PR fix or reference?

<!-- Include any related issues from Podman Desktop
repository (or from another issue tracker). -->

N/A

### How to test this PR?

Add:

```
```mermaid
graph TD;
    A-->B;
    A-->C;
    B-->D;
    C-->D;
```
```

To an example markdown page.

<!-- Please explain steps to reproduce -->

Signed-off-by: Charlie Drage <[email protected]>

website/docusaurus.config.js

@@ -18,6 +18,10 @@ const config = {
   projectName: 'podman-desktop',
   deploymentBranch: 'gh-pages',
   trailingSlash: false,
+  markdown: {
+    mermaid: true,
+  },
+  themes: ['@docusaurus/theme-mermaid'],
   plugins: [
     async () => {
       return {

website/package.json

@@ -24,6 +24,7 @@
   "dependencies": {
     "@docusaurus/core": "2.4.1",
     "@docusaurus/preset-classic": "2.4.1",
+    "@docusaurus/theme-mermaid": "^2.4.1",
     "@fortawesome/fontawesome-svg-core": "^6.4.2",
     "@fortawesome/free-brands-svg-icons": "^6.4.2",
     "@fortawesome/free-solid-svg-icons": "^6.4.2",