Add troubleshooting instructions for prometheus-operator referencing the FAQ for easier discovery (#15714)

**Description**
Adding documentation for troubleshooting install error already
documented in the FAQ
⚒️ Fixes  # <!--(issue)-->

**⚙️ Type of change**

- [x] ⚙️ Feature/App addition
- [ ] 🪛 Bugfix
- [ ] ⚠️ Breaking change (fix or feature that would cause existing
functionality to not work as expected)
- [ ] 🔃 Refactor of current code

**🧪 How Has This Been Tested?**
Preview of .md file inspected

**📃 Notes:**
<!-- Please enter any other relevant information here -->

**✔️ Checklist:**

- [ ] ⚖️ My code follows the style guidelines of this project
- [ ] 👀 I have performed a self-review of my own code
- [ ] #️⃣ I have commented my code, particularly in hard-to-understand
areas
- [✔️] 📄 I have made corresponding changes to the documentation
- [ ] ⚠️ My changes generate no new warnings
- [ ] 🧪 I have added tests to this description that prove my fix is
effective or that my feature works
- [ ] ⬆️ I increased versions for any altered app according to semantic
versioning

**➕ App addition**

If this PR is an app addition please make sure you have done the
following.

- [ ] 🪞 I have opened a PR on
[truecharts/containers](https://github.com/truecharts/containers) adding
the container to TrueCharts mirror repo.
- [ ] 🖼️ I have added an icon in the Chart's root directory called
`icon.png`

---

_Please don't blindly check all the boxes. Read them and only check
those that apply.
Those checkboxes are there for the reviewer to see what is this all
about and
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---------

Signed-off-by: vdudas <vlad@analogcoast.com>
Signed-off-by: Kjeld Schouten <kjeld@schouten-lebbing.nl>
Co-authored-by: Kjeld Schouten <kjeld@schouten-lebbing.nl>

charts/operators/prometheus-operator/docs/installation.md

@@ -0,0 +1,22 @@
+# Troubleshooting
+## INSTALLATION FAILED: rendered manifests contain a resource that already exists
+
+### TrueNAS SCALE
+
+If you get
+
+![Error message: [EFAULT] Failed to install App: Error: INSTALLATION FAILED: rendered manifests contain a resource that already exists. Unable to continue with install: CustomResourceDefinition "alertmanagerconfigs.monitoring.coreos.com" in namespace "" exists and cannot be imported into the current release: invalid ownership metadata; label validation error: missing key "app.kubernetes.io/managed-by": must be set to "Helm"; annotation validation error: missing key "meta.helm.sh/release-name": must be set to "prometheus-operator"; annotation validation error: missing key "meta.helm.sh/release-namespace": must be set to "ix-prometheus-operator"](images/install_error_message.webp)
+
+>[EFAULT] Failed to install App: Error: INSTALLATION FAILED: rendered manifests contain a resource that already exists. Unable to continue with install: CustomResourceDefinition "alertmanagerconfigs.monitoring.coreos.com" in namespace "" exists and cannot be imported into the current release: invalid ownership metadata; label validation error: missing key "app.kubernetes.io/managed-by": must be set to "Helm"; annotation validation error: missing key "meta.helm.sh/release-name": must be set to "prometheus-operator"; annotation validation error: missing key "meta.helm.sh/release-namespace": must be set to "ix-prometheus-operator"
+
+you should follow instructions from the [FAQ](https://truecharts.org/manual/FAQ#prometheus-operator) to resolve it
+
+### Helm
+
+
+On Helm this indicates your previously had a non-TrueCharts version of Prometheus-Operator installed.
+Please uninstall all old CRD's before installing our version of Prometheus Operator.
+
+If you don't know how, this might be a good moment to do some research or ask yourself if running DIY clusters is a good idea for your specific knowlage level.
+
+