Increase default timeout for instance creation\update and improve doc (#8161) (#14909)

Signed-off-by: Modular Magician <[email protected]>

Author: modular-magician

.changelog/8161.txt

@@ -0,0 +1,3 @@
+```release-note:enhancement
+increase default timeout for instance operations to 1 hour
+```

google/services/bigtable/resource_bigtable_instance.go

@@ -31,8 +31,8 @@ func ResourceBigtableInstance() *schema.Resource {
 		},
 
 		Timeouts: &schema.ResourceTimeout{
-			Create: schema.DefaultTimeout(20 * time.Minute),
-			Update: schema.DefaultTimeout(20 * time.Minute),
+			Create: schema.DefaultTimeout(60 * time.Minute),
+			Update: schema.DefaultTimeout(60 * time.Minute),
 		},
 
 		CustomizeDiff: customdiff.All(

website/docs/r/bigtable_instance.html.markdown

@@ -148,8 +148,10 @@ In addition to the arguments listed above, the following computed attributes are
 This resource provides the following
 [Timeouts](https://developer.hashicorp.com/terraform/plugin/sdkv2/resources/retries-and-customizable-timeouts) configuration options:
 
-- `create` - Default is 20 minutes.
-- `update` - Default is 20 minutes.
+- `create` - Default is 60 minutes.
+- `update` - Default is 60 minutes.
+
+Adding clusters to existing instances can take a long time. Consider setting a higher value to timeouts if you plan on doing that.
 
 ## Import