auth: add env and ini var for mount_point option

This makes most sense; it is part of the credentials needed to
authenticate with vault, e.g. on servers with multiple independent
AppRole mountpoints.

plugins/doc_fragments/auth.py

@@ -122,6 +122,17 @@ class ModuleDocFragment(object):
         vars:
           - name: ansible_hashi_vault_auth_method
             version_added: 1.2.0
+      mount_point:
+        env:
+          - name: ANSIBLE_HASHI_VAULT_MOUNT_POINT
+            version_added: 1.5.0
+        ini:
+          - section: hashi_vault_collection
+            key: mount_point
+            version_added: 1.5.0
+        vars:
+          - name: ansible_hashi_vault_mount_point
+            version_added: 1.5.0
       token:
         env:
           - name: ANSIBLE_HASHI_VAULT_TOKEN