storage: GenericEphemeralVolume

This is the initial documentation for one new feature:
- https://github.com/kubernetes/enhancements/issues/1698

A new page gets created for different ephemeral volumes because the
relationship between them needs to be explained.

Co-authored-by: Tim Bannister <tim@scalefactory.com>

content/en/docs/reference/command-line-tools-reference/feature-gates.md

@@ -101,6 +101,7 @@ different Kubernetes components.
 | `ExperimentalHostUserNamespaceDefaulting` | `false` | Beta | 1.5 | |
 | `EvenPodsSpread` | `false` | Alpha | 1.16 | 1.17 |
 | `EvenPodsSpread` | `true` | Beta | 1.18 | |
+| `GenericEphemeralVolume` | `false` | Alpha | 1.19 | |
 | `HPAScaleToZero` | `false` | Alpha | 1.16 | |
 | `HugePageStorageMediumSize` | `false` | Alpha | 1.18 | 1.18 |
 | `HugePageStorageMediumSize` | `true` | Beta | 1.19 | |
@@ -431,6 +432,7 @@ Each feature gate is designed for enabling/disabling a specific feature:
    use EndpointSlices as the primary data source instead of Endpoints, enabling
    scalability and performance improvements. See [Enabling Endpoint Slices](/docs/tasks/administer-cluster/enabling-endpointslices/).
 - `GCERegionalPersistentDisk`: Enable the regional PD feature on GCE.
+- `GenericEphemeralVolume`: Enables ephemeral, inline volumes that support all features of normal volumes (can be provided by third-party storage vendors, storage capacity tracking, restore from snapshot, etc.). See [Ephemeral Volumes](/docs/concepts/storage/ephemeral-volumes/).
 - `HugePages`: Enable the allocation and consumption of pre-allocated [huge pages](/docs/tasks/manage-hugepages/scheduling-hugepages/).
 - `HugePageStorageMediumSize`: Enable support for multiple sizes pre-allocated [huge pages](/docs/tasks/manage-hugepages/scheduling-hugepages/).
 - `HyperVContainer`: Enable [Hyper-V isolation](https://docs.microsoft.com/en-us/virtualization/windowscontainers/manage-containers/hyperv-container) for Windows containers.