fix(ollama): accept `prompt` alias on /api/embed for Ollama parity (#9780)

Ollama's embedding endpoint accepts both `input` and `prompt` as the
input string value (see ollama/ollama docs/api.md#generate-embeddings).
LocalAI only accepted `input`, which broke client libraries that send
the `prompt` form.

Add `Prompt` to OllamaEmbedRequest and have GetInputStrings fall back
to it when Input is unset. Input still wins when both are provided.

Fixes #9767.

Assisted-by: Claude:claude-opus-4-7 [Claude Code]

Signed-off-by: Ettore Di Giacinto <mudler@localai.io>
Co-authored-by: Ettore Di Giacinto <mudler@localai.io>