Add a note that users cannot send a duplicate tuples in the Write request (even if in writes and deletes)

[rhamzeh]

We should add a note in the transactional writes page that people cannot send duplicate tuples in the same request, even if they are across the delete/write

Example:
Request:

curl 'http://localhost:8080/stores/01JEC6JK6SNE650REAQYZ71CA5/write' \
  -H 'content-type: application/json' \
  --data-raw '{"authorization_model_id":"01JFGY272ZPRS9ARXD4F3D6GP9","writes":{"tuple_keys":[{"user":"user:anne","relation":"member","object":"group:2"}]},"deletes":{"tuple_keys":[{"user":"user:anne","relation":"member","object":"group:2"}]}}'

Response:

{"code":"cannot_allow_duplicate_tuples_in_one_request","message":"duplicate tuple in write: user: 'user:anne', relation: 'member', object: 'group:2'"}

Ref: https://cloud-native.slack.com/archives/C06G1NNH47N/p1734660203048149