clarify that user-specified ids are only required on management plane requests (#1250)

Author: andrei-scripniciuc

aip/general/0133.md

@@ -96,7 +96,8 @@ message CreateBookRequest {
   - The field **should** be [annotated as required][aip-203].
   - The field **must** identify the [resource type][aip-123] of the resource
     being created.
-- A `{resource}_id` field **must** be included.
+- A `{resource}_id` field **must** be included for management plane resources,
+  and **should** be included for data plane resources.
 - The resource field **must** be included and **must** map to the POST body.
 - The request message **must not** contain any other required fields and
   **should not** contain other optional fields except those described in this
@@ -217,6 +218,7 @@ name and use it in references from other resources.
 
 ## Changelog
 
+- **2023-10-20**: Clarify that {resource}_id is only required for management plane resources.
 - **2023-08-24**: Adding consistency requirement.
 - **2023-05-11**: Changing guidance around resource_id to a must.
 - **2022-11-04**: Referencing aggregated error guidance in AIP-193, similar to