docs(cert-manager): Add How-To guide (#8084)

**Description**

Added docs for `cert-manager`, thanks to @xstar97 and @malcolmcdixon for
contributions to the doc also

⚒️ Fixes  # <!--(issue)-->

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- [X] ⚙️ Feature/App addition
- [ ] 🪛 Bugfix
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- [ ] 🔃 Refactor of current code

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charts/enterprise/cert-manager/docs/how-to.md

@@ -0,0 +1,52 @@
+# Cert-Manager Setup Guide
+
+This guide will walk you through setting up `cert-manager`, certificate management for Kubernetes.
+
+## Prerequisites
+
+Ensure you have the `enterprise` train enabled for `TrueCharts` as discussed [here](https://truecharts.org/manual/SCALE/guides/getting-started/#adding-truecharts).
+
+Search for cert-manager in the `Apps` menu | `Available Applications` tab and click **Install**.
+
+## Cloudflare DNS-Provider
+
+You can setup multiple domains with a single cert-manager app, all you have to do is either add the global API key (**not recommended**) or `Add` multiple `ACME Issuer` entries for each domain and create an API token for each at [Cloudflare API Tokens](https://dash.cloudflare.com/profile/api-tokens).
+
+- Give the certificate a name (eg domain or "maincert", etc).
+- Select the correct provider, for example `Cloudflare`.
+- Set **Server** to **Letsencrypt-Production**.
+- Set Email to the account email.
+- Optionally set Cloudflare API key (**not recommended**)
+- Set the Cloudflare API Token to the one created earlier.
+
+![cert-manager1](img/cert-manager1.png)
+
+## cert-manager App
+
+> **Note**
+>
+> It is normal that the app does not run, there are no events, no logs and no shell. This is by design.
+
+![cert-manager3](img/cert-manager3.png)
+
+## How to Add Ingress to Apps with cert-manager
+
+Here's an example on how to add ingress to an app with cert-manager for a single domain only.
+
+Add the name of the `ACME Issuer` into `Cert-Manager clusterIssuer`
+
+> **Warning**
+> Do **NOT** use this combined with the `TLS-Settings`.
+
+![cert-manager2](img/cert-manager2.png)
+
+If you want to support multiple domains, use the `TLS-Settings` option to create each one, basically an extra step each time.
+
+## Verifying cert-manager is working
+
+Once install using the Ingress settings above, you can see the `Application Events` for the app in question to pull the certificate and issue the challenge directly. See the example below:
+
+![cert-manager4](img/cert-manager4.png)
+![cert-manager5](img/cert-manager5.png)
+
+All is automated by `cert-manager`