feat: Add support for Mermaid diagrams

[JakeSCahill]

This PR allows us to use the antora-meramid-extension to define Mermaid diagrams in the docs and have them rendered in the build output.

Example:

[mermaid]
....
flowchart TB

%% Define classes
classDef userAction stroke:#374D7C, fill:#E2EBFF, font-weight:bold,rx:5,ry:5
classDef systemAction fill:#F6FBF6,stroke:#25855a,stroke-width:2px,color:#20293c,rx:5,ry:5

%% -- LEGEND SUBGRAPH --
subgraph Legend
  direction TB
  UA([User Action]):::userAction
  SE([System Event]):::systemAction
end

%% -- MAIN FLOWCHART --
A((Start)):::systemAction --> B["Check replication factor (≥3) and PDB"]:::userAction
B --> C["Decommission broker"]:::userAction
C --> D["Data migrates to other replicas"]:::systemAction
D --> E["Delete PVC (local PV)"]:::userAction
E --> F["Cordon & drain node"]:::userAction
F --> G["Broker shuts down gracefully"]:::systemAction
G --> H["Upgrade node"]:::userAction
H --> I["New broker Pod and new PVC (local PV)"]:::systemAction
I --> J["Data rebalances"]:::systemAction
J --> K((Cluster healthy)):::systemAction
....

Result:

[netlify]

✅ Deploy Preview for docs-ui ready!

Name	Link
🔨 Latest commit	d7bf784
🔍 Latest deploy log	https://app.netlify.com/sites/docs-ui/deploys/678e7bffd733660008194145
😎 Deploy Preview	https://deploy-preview-244--docs-ui.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site configuration.

[Deflaimun]

Nice addition!