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/network/system/net_banner.py

@@ -33,7 +33,6 @@ options:
       - The banner text that should be
         present in the remote device running configuration.  This argument
         accepts a multiline string, with no empty lines. Requires I(state=present).
-    default: null
   state:
     description:
       - Specifies whether or not the configuration is

lib/ansible/modules/network/system/net_ping.py

@@ -27,7 +27,6 @@ options:
   count:
     description:
     - Number of packets to send.
-    required: false
     default: 5
   dest:
     description:
@@ -36,8 +35,6 @@ options:
   source:
     description:
     - The source IP Address.
-    required: false
-    default: null
   state:
     description:
     - Determines if the expected result is success or fail.
@@ -46,7 +43,6 @@ options:
   vrf:
     description:
     - The VRF to use for forwarding.
-    required: false
     default: default
 notes:
   - For Windows targets, use the M(win_ping) module instead.