Clarify description of filter_expr (#4161) (#2653)

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

Author: modular-magician

.changelog/4161.txt

@@ -0,0 +1,3 @@
+```release-note:REPLACEME
+
+```

google-beta/resource_compute_subnetwork.go

@@ -133,7 +133,8 @@ lasting connections. Default is an interval of 5 seconds per connection. Default
 							Type:     schema.TypeString,
 							Optional: true,
 							Description: `Export filter used to define which VPC flow logs should be logged, as as CEL expression. See
-https://cloud.google.com/vpc/docs/flow-logs#filtering for details on how to format this field.`,
+https://cloud.google.com/vpc/docs/flow-logs#filtering for details on how to format this field.
+The default value is 'true', which evaluates to include everything.`,
 							Default:      "true",
 							AtLeastOneOf: []string{"log_config.0.aggregation_interval", "log_config.0.flow_sampling", "log_config.0.metadata", "log_config.0.filter_expr"},
 						},

website/docs/r/compute_subnetwork.html.markdown

@@ -279,6 +279,7 @@ The `log_config` block supports:
   (Optional)
   Export filter used to define which VPC flow logs should be logged, as as CEL expression. See
   https://cloud.google.com/vpc/docs/flow-logs#filtering for details on how to format this field.
+  The default value is 'true', which evaluates to include everything.
 
 ## Attributes Reference