Clean up module documentation (#36909)

* Clean up module documentation

This PR includes:
- Removal of `default: None` (and variations)
- Removal of `required: false`
- Fixing booleans and `type: bool` where required

* Fix remaining (new) validation issues

lib/ansible/modules/cloud/amazon/ec2_vpc_subnet.py

@@ -24,66 +24,55 @@ options:
   az:
     description:
       - "The availability zone for the subnet."
-    required: false
-    default: null
   cidr:
     description:
       - "The CIDR block for the subnet. E.g. 192.0.2.0/24."
-    required: false
-    default: null
   ipv6_cidr:
     description:
       - "The IPv6 CIDR block for the subnet. The VPC must have a /56 block assigned and this value must be a valid IPv6 /64 that falls in the VPC range."
       - "Required if I(assign_instances_ipv6=true)"
-    required: false
-    default: null
     version_added: "2.5"
   tags:
     description:
       - "A dict of tags to apply to the subnet. Any tags currently applied to the subnet and not present here will be removed."
-    required: false
-    default: null
     aliases: [ 'resource_tags' ]
   state:
     description:
       - "Create or remove the subnet"
-    required: false
     default: present
     choices: [ 'present', 'absent' ]
   vpc_id:
     description:
       - "VPC ID of the VPC in which to create or delete the subnet."
     required: true
-    default: null
   map_public:
     description:
-      - "Specify true to indicate that instances launched into the subnet should be assigned public IP address by default."
-    required: false
-    default: false
+      - "Specify C(yes) to indicate that instances launched into the subnet should be assigned public IP address by default."
+    type: bool
+    default: 'no'
     version_added: "2.4"
   assign_instances_ipv6:
     description:
-      - "Specify true to indicate that instances launched into the subnet should be automatically assigned an IPv6 address."
-    required: false
-    default: false
+      - "Specify C(yes) to indicate that instances launched into the subnet should be automatically assigned an IPv6 address."
+    type: bool
+    default: 'no'
     version_added: "2.5"
   wait:
     description:
       - "When specified,I(state=present) module will wait for subnet to be in available state before continuing."
-    required: false
-    default: true
+    type: bool
+    default: 'yes'
     version_added: "2.5"
   wait_timeout:
     description:
       - "Number of seconds to wait for subnet to become available I(wait=True)."
-    required: false
     default: 300
     version_added: "2.5"
   purge_tags:
     description:
-      - Whether or not to remove tags that do not appear in the I(tags) list. Defaults to true.
-    required: false
-    default: true
+      - Whether or not to remove tags that do not appear in the I(tags) list.
+    type: bool
+    default: 'yes'
     version_added: "2.5"
 extends_documentation_fragment:
     - aws