docs: add highlights for 0.9 release

This describes high-level new features in Talos 0.9.

Signed-off-by: Andrey Smirnov <smirnov.andrey@gmail.com>

website/content/docs/v0.9/Introduction/what-is-new.md

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+---
+title: What's New in Talos 0.9
+weight: 5
+---
+
+## Control Plane as Static Pods
+
+Talos now runs Kubernetes control plane as static pods managed via machine configuration.
+This change makes bootstrap process much more stable and resilient to failures.
+For single control plane node clusters it eliminates bugs with control plane being unavailable after a reboot.
+As control plane configuration is managed via Talos API, even if control plane configuration was wrong and
+API server is not available, change can be rolled back using `talosctl` to bring the control plane back up.
+When upgrading from Talos 0.8, control plane can be [converted](../Guides/converting-control-plane/) to run as static pods.
+
+## ECDSA Certificates and Keys for Kubernetes
+
+Talos now generates uses ECDSA keys for Kubernetes and etcd PKI.
+ECDSA keys are much smaller and all PKI operations are much faster (for example, generating certificate from the CA) which
+leads to much faster bootstrap and boot times.
+
+## Immediate Machine Configuration Updates
+
+Changes to `.cluster` part of Talos machine configuration can now be applied immediately (without a reboot).
+This allows for example updating versions of control plane components, adding additional arguments or modifying bootstrap manifests.
+Future versions of Talos will expand on that to allow most of the machine configuration to be applied without a reboot.
+
+## Disk Encryption
+
+Talos now supports encryption for `STATE` and `EPHEMERAL` partitions of the system disk.
+`STATE` partition holds machine configuration and `EPHEMERAL` partition is mounted as `/var` which stores container runtime
+state, configuration files laid on top of Talos read-only immutable root filesystem.
+Encryption key in Talos 0.9 is derived from the Node UUID which is unique machine identifier provided by the manufacturer.
+Disk encryption is not enabled by default, it needs to be [enabled](../Guides/disk-encryption/) via machine configuration.
+
+## Virtual IP for the Control Plane Endpoint
+
+Talos adds support for Virtual L2 shared IP for the control plane: control plane nodes make sure only one of the nodes
+adverties shared IP via ARP.
+If one of the control plane nodes goes down, another node takes over shared IP.
+
+## Updated Components
+
+Linux: 5.10.1 -> 5.10.19
+
+Kubernetes: 1.20.1 -> 1.20.4
+
+CoreDNS: 1.7.0 -> 1.8.0
+
+etcd: 3.4.14 -> 3.4.15
+
+containerd: 1.4.3 -> 1.4.4