add docs for profile_options

docs/docs/explanations/advanced-profiles-settings.md

@@ -15,14 +15,27 @@ Profiles are used to control the JupyterLab user instances and Dask workers prov
 profiles:
   jupyterlab:
     - display_name: Small Instance
-      description: Stable environment with 1 cpu / 1 GB ram
+      description: Stable environment with 2 cpu / 8 GB ram
       access: all
       default: true
+      profile_options:  # optional
+        image:
+          display_name: Image
+          choices:
+            default:
+              display_name: nebari-jupyterlab:latest
+              default: true
+              kubespawner_override:
+                image: quay.io/nebari/nebari-jupyterlab:latest
+            custom:
+              display_name: my-custom-image:mytag
+              kubespawner_override:
+                image: <my-container-registry>/myOrg/my-custom-image:mytag
       kubespawner_override:
-        cpu_limit: 1
-        cpu_guarantee: 1
-        mem_limit: 1G
-        mem_guarantee: 1G
+        cpu_limit: 2
+        cpu_guarantee: 1.5
+        mem_limit: 8G
+        mem_guarantee: 6G
     - display_name: Medium Instance
     ...
 ```
@@ -35,6 +48,8 @@ Each profile under `jupyterlab` is a named JupyterLab profile.
 
 `description` is a description of the profile that will be displayed to users.
 
+`profile_options` makes it possible to set various sub-options per profile. See the [Kubespawner docs](https://jupyterhub-kubespawner.readthedocs.io/en/latest/spawner.html#kubespawner.KubeSpawner.profile_list) for more info.
+
 `kubespawner_override` field to define behavior as per the [KubeSpawner](https://jupyterhub-kubespawner.readthedocs.io/en/latest/spawner.html) API.
 
 It is possible to control which users have access to which JupyterLab profiles. Each profile has a field named `access` which can be set to `all` (default if omitted), `yaml`, or