Add config parameter for gcp to customize the snapshot location

Signed-off-by: Cyrill Troxler <cyrill@nine.ch>

docs/api-types/volumesnapshotlocation.md

@@ -52,9 +52,15 @@ The configurable parameters are as follows:
 
 #### GCP
 
-No parameters required.
+##### config
+
+| Key | Type | Default | Meaning |
+| --- | --- | --- | --- |
+| `snapshotLocation` | string | Empty | *Example*: "us-central1"<br><br>See [GCP documentation][4] for the full list.<br><br>If not specified the snapshots are stored in the [default location][5]. |
 
 [0]: #aws
 [1]: #gcp
 [2]: #azure
 [3]: http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/using-regions-availability-zones.html#concepts-available-regions
+[4]: https://cloud.google.com/storage/docs/locations#available_locations
+[5]: https://cloud.google.com/compute/docs/disks/create-snapshots#default_location

docs/gcp-config.md

@@ -140,6 +140,10 @@ Specify the following values in the example files:
 
   * Uncomment the `--default-volume-snapshot-locations` and replace provider locations with the values for your environment.
 
+* (Optional) In file `config/gcp/06-volumesnapshotlocation.yaml`:
+
+  * Add `snapshotLocation: <YOUR_LOCATION>` to the config. See the [VolumeSnapshotLocation definition][8] for details.
+
 ## Start the server
 
 In the root of your Velero directory, run:
@@ -152,6 +156,7 @@ In the root of your Velero directory, run:
 
   [0]: namespace.md
   [7]: api-types/backupstoragelocation.md#gcp
+  [8]: api-types/volumesnapshotlocation.md#gcp
   [15]: https://cloud.google.com/compute/docs/access/service-accounts
   [16]: https://cloud.google.com/sdk/docs/
   [20]: faq.md