[CentralDashboard] Docs added for central-dashboard (#1538)

* Kubeflow Central-Dashboard docs added, and registration flow docs added with GIF

* Links to now point to multi-user-isolation docs, details about Central-Dashboard added to component

* Addressed all code comments by @sarahmaddox

* Updated the title for Central-Dashboard, updated the steps for registration-view

* Numbered bullets for reg-flow and Formatting

content/docs/components/central-dash/_index.md

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+title = "Central Dashboard"
+description = "The central user interface (UI) in Kubeflow"
+weight = 35
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content/docs/components/central-dash/overview.md

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+title = "Central Dashboard"
+description = "An overview of the Kubeflow user interface (UI)"
+weight = 10
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+
+Your Kubeflow deployment includes Central Dashboard as a key component to provide quick access to all components deployed in your cluster. Some features include:
+
+- Quick action, pipelines cards, metrics, and high level kubernetes events for an overview of your jobs and cluster in one view
+- Housing view for all sub services running inside the cluster: `Pipelines`, `Katib`, `Notebooks`, etc.
+- Helps users ramp up their environment with a [registration flow](/docs/components/central-dash/registration-flow/) (for multi-user isolation, or the first namespace for a shared deployment)
+- Allows you to [manage your own namespaces (workgroups)](/docs/other-guides/multi-user-overview/).

content/docs/components/central-dash/registration-flow.md

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+title = "Registration Flow"
+description = "The view that allows you to set up your first namespace in the cluster"
+weight = 10
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+
+Your Kubeflow deployment comes deployed with Kubeflow Central Dashboard. 
+
+This view will show when the cluster is:
+
+- When in `multi-user` isolation mode:
+  - Your user has no profile (workgroup / namespace) role-bindings in which you're `admin` (Owner)
+- When in `single-user` isolation mode:
+  - The entire cluster has no profile (workgroup / namespace) role-bindings
+
+This guide shows you what this view looks like and how the flow appears.
+
+## Quick guide
+Summary of steps:
+
+1. Follow the [Kubeflow getting-started guide](/docs/started/getting-started/) 
+  to set up your Kubeflow deployment and open the Kubeflow UI.
+1. If the registration flow view shows up (because the conditions above are satisfied), follow the guide below, else your network should be good to use as is
+
+## Steps
+
+1. On page load the Registration View opens up
+   - This view will walk you through creating the first workgroup binding for your user or cluster (depending on `isolation-mode`)
+1. Since you don't have an owned namespace, we will create one
+   - IE. the user does not have `admin` profile/workgroup binding for a namespace
+1. A default name for your new namespace is auto-filled in the input box (the default name is your LDAP)
+   - LDAP for an email like `kubeflow-user@google.com` would be `kubeflow-user`
+   - If there are errors on this step, like invalid name or namespace already exists, you will see an error and the input box will turn red, you can then try again
+1. Once you successfully create the namespace, you should be greeted the Kubeflow Dashboard overview page
+
+## Visual
+![Kubeflow registration flow](/docs/images/registration-flow.gif)