Declare batched input support for OpenAI embeddings

[liuzemei]

Q	A
Bug fix?	yes
New feature?	no
Docs?	no
Issues	Fix #2127
License	MIT

OpenAI embedding models accept an array input and the existing model client forwards array payloads correctly. This adds Capability::INPUT_MULTIPLE to the OpenAI embedding catalog entries so vectorization can use a single batched request for multiple strings.

Tests:

./vendor/bin/phpunit Tests/ModelCatalogTest.php
./vendor/bin/phpunit Tests/Embeddings/ModelClientTest.php
./vendor/bin/phpunit
./vendor/bin/phpstan analyse --no-progress --memory-limit=1G