chore: add offset-based pagination support to aibridge list endpoint (#20393)

Necessary for the frontend to be able to paginate easily. Cursor
pagination is good for fetching all events, but doesn't play very well
when a pagination component gets involved.

Adds support for `?offset=x` to the existing endpoint. The cursor-based
pagination (`?after_id=x`) is still supported. The two pagination modes
are mutually exclusive, and are documented as such. If both are
supplied, the request will be rejected.

Also adds a `total` property to the response that contains the full
count of items matching the filter. We already have indices in place so
I don't think this will impact performance (or we can revisit it before
GA).

coderd/apidoc/swagger.json

@@ -91,9 +91,15 @@
 					},
 					{
 						"type": "string",
-						"description": "Cursor pagination after ID",
+						"description": "Cursor pagination after ID (cannot be used with offset)",
 						"name": "after_id",
 						"in": "query"
+					},
+					{
+						"type": "integer",
+						"description": "Offset pagination (cannot be used with after_id)",
+						"name": "offset",
+						"in": "query"
 					}
 				],
 				"responses": {
@@ -10427,6 +10433,9 @@
 					"items": {
 						"$ref": "#/definitions/codersdk.AIBridgeInterception"
 					}
+				},
+				"total": {
+					"type": "integer"
 				}
 			}
 		},