fix(archivebox): Remove unused postgres section from questions.yaml, add docs (#18488)

**Description**

The `postgres` section in `questions.yaml` was added by accident in the
[original new chart PR](https://github.com/truecharts/charts/pull/18258)
because I copy-pasted a template from an existing project to modify and
didn't notice that line.

Additional minor changes included:

- enable pod `liveness` `probe` on `/health/` by default
- explicitly set `runAsNonRoot: false` and ingress port `protocol: http`
- add new `docs/installation_guide.md`

**⚙️ Type of change**

- [ ] ⚙️ Feature/App addition
- [x] 📖 Documentation addition
- [x] 🪛 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?**

Tested in TrueNAS scale by installing incubator chart `archivebox` and
setting postgres instaces to 0.

**📝 Notes:**

I still need help with a `missing Chart.yaml` error to get this working:
-
https://github.com/truecharts/charts/pull/18258#issuecomment-1958457400
-
https://www.reddit.com/r/truenas/comments/1awtcbw/help_with_contributing_new_archivebox_chart/

**✔️ Checklist:**

- [x] ⚖️ My code follows the style guidelines of this project
- [x] 👀 I have performed a self-review of my own code
- [x] #️⃣ I have commented my code, particularly in hard-to-understand
areas
- [x] 📄 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

---------

Signed-off-by: Nick Sweeting <github@sweeting.me>
Signed-off-by: Kjeld Schouten <info@kjeldschouten.nl>
Co-authored-by: Kjeld Schouten <info@kjeldschouten.nl>

charts/incubator/archivebox/values.yaml

@@ -10,6 +10,7 @@ config:
 securityContext:
   container:
     readOnlyRootFilesystem: false
+    runAsNonRoot: false
     runAsGroup: 0
     runAsUser: 0
 
@@ -18,6 +19,7 @@ service:
     ports:
       main:
         port: 9598
+        protocol: http
         targetPort: 8000
 
 workload:
@@ -25,6 +27,10 @@ workload:
     podSpec:
       containers:
         main:
+          probes:
+            liveness:
+              type: http
+              path: /health/
           env:
             ADMIN_USERNAME: "{{ .Values.config.admin_username }}"
             ADMIN_PASSWORD: "{{ .Values.config.admin_password }}"