doc: Update descriptions for Collection and DB properties to clarify usage of empty strings

Author: EspenAlbert

cfn-resources/custom-db-role/docs/resource.md

@@ -28,7 +28,7 @@ To declare this entity in your AWS CloudFormation template, use the following sy
 
 #### Collection
 
-Human-readable label that identifies the collection on which you grant the action to one MongoDB user. If you don't set this parameter, you grant the action to all collections in the database specified in the actions.resources.db parameter. If you set "actions.resources.cluster" : true, MongoDB Cloud ignores this parameter.
+Human-readable label that identifies the collection on which you grant the action to one MongoDB user. If you don't set this parameter, you grant the action to all collections in the database specified in the actions.resources.db parameter. If you set "actions.resources.cluster" : true, MongoDB Cloud ignores this parameter. Use the empty string ("") to allow an action on all collections.
 
 _Required_: No
 
@@ -38,7 +38,7 @@ _Update requires_: [No interruption](https://docs.aws.amazon.com/AWSCloudFormati
 
 #### DB
 
-Human-readable label that identifies the database on which you grant the action to one MongoDB user. If you set "actions.resources.cluster" : true, MongoDB Cloud ignores this parameter.
+Human-readable label that identifies the database on which you grant the action to one MongoDB user. If you set "actions.resources.cluster" : true, MongoDB Cloud ignores this parameter. Use the empty string ("") to allow an action on all databases.
 
 _Required_: No
 

cfn-resources/custom-db-role/mongodb-atlas-customdbrole.json

@@ -20,11 +20,11 @@
       "properties": {
         "Collection": {
           "type": "string",
-          "description": "Human-readable label that identifies the collection on which you grant the action to one MongoDB user. If you don't set this parameter, you grant the action to all collections in the database specified in the actions.resources.db parameter. If you set \"actions.resources.cluster\" : true, MongoDB Cloud ignores this parameter."
+          "description": "Human-readable label that identifies the collection on which you grant the action to one MongoDB user. If you don't set this parameter, you grant the action to all collections in the database specified in the actions.resources.db parameter. If you set \"actions.resources.cluster\" : true, MongoDB Cloud ignores this parameter. Use the empty string (\"\") to allow an action on all collections."
         },
         "DB": {
           "type": "string",
-          "description": "Human-readable label that identifies the database on which you grant the action to one MongoDB user. If you set \"actions.resources.cluster\" : true, MongoDB Cloud ignores this parameter."
+          "description": "Human-readable label that identifies the database on which you grant the action to one MongoDB user. If you set \"actions.resources.cluster\" : true, MongoDB Cloud ignores this parameter. Use the empty string (\"\") to allow an action on all databases."
         },
         "Cluster": {
           "type": "boolean",