[Feature] Introduce Model

### Search before asking

- [x] I searched in the [issues](https://github.com/apache/paimon/issues) and found nothing similar.

### Motivation

Current Flink is working on supporting ML models in SQL(ps: [Flip](https://cwiki.apache.org/confluence/display/FLINK/FLIP-437%3A+Support+ML+Models+in+Flink+SQL)). as Paimon could provide model metadata in a standard format that supports ML models for engines.

### Solution

#### Spec
| Field | Type | Comment |
|---|---|---|
| name | String | name |
| comment |String | comment|
| options | Map | properties |
| inputParams | `Optional>` | parameters |
| returnParams | `Optional>` | result |

### Anything else?

_No response_

### Are you willing to submit a PR?

- [ ] I'm willing to submit a PR!

No files, tests, or implementation entry points are identified. Start by reviewing the proposed model metadata fields and the linked Flink FLIP-437 specification. Done should mean Paimon can provide model metadata in a standard format, including name, comment, options, input parameters, and return parameters.

Written by the indexing model from the issue text.