update alerts custom documentation (#581)

Author: jdu2600

custom_documentation/doc/endpoint/alerts/windows/windows_shellcode_thread.md

@@ -28,6 +28,7 @@ This alert is generated when a Shellcode Threat alert occurs.
 | Memory_protection.parent_to_child |
 | Memory_protection.self_injection |
 | Memory_protection.unique_key_v1 |
+| Memory_protection.unique_key_v2 |
 | Responses.@timestamp |
 | Responses.action.action |
 | Responses.action.file.attributes |

custom_documentation/src/endpoint/data_stream/alerts/windows/windows_shellcode_thread.yaml

@@ -33,6 +33,7 @@ fields:
   - Memory_protection.parent_to_child
   - Memory_protection.self_injection
   - Memory_protection.unique_key_v1
+  - Memory_protection.unique_key_v2
   - Responses.@timestamp
   - Responses.action.action
   - Responses.action.file.attributes