[Feature][Connector] Add Informix CDC Connector

## Background
IBM Informix is a relational database widely used in financial institutions, retail chains, and legacy enterprise systems, especially in banking core systems and point-of-sale (POS) applications.

SeaTunnel currently supports Informix via the JDBC connector (dialect-based). However, JDBC-based reading cannot provide CDC, and it cannot leverage Informix-specific capabilities (for example, fragmentation-aware reads) for better performance.

## Motivation
- **Legacy system integration**: Informix remains mission-critical in many industries.
- **Multi-table CDC**: Sync multiple tables in one job to modern platforms.
- **Performance**: JDBC cannot utilize Informix fragmentation/parallelism effectively.
- **Near real-time**: CDC is required for timely analytics and replication.

## Current Status vs. Proposed Enhancement

| Feature | Current (JDBC Connector) | Proposed (Informix-CDC Source) |
| :--- | :--- | :--- |
| Read | Snapshot | Snapshot + CDC |
| CDC | No | Yes (API / log / trigger based) |
| Multi-Table | Limited (depends on connector) | Yes (CDC multi-table patterns) |
| Optimizations | Generic | Informix-aware (when available) |
| Data Types | Basic (limited) | SERIAL8, LVARCHAR, Smart LOBs |

## Proposed Solution
Implement a dedicated **Informix-CDC** Source connector.

### Why not `table_list`?
For CDC connectors in SeaTunnel, multi-table selection and per-table overrides are typically done via:
- `table-names` / `table-pattern` (choose tables)
- `table-names-config` (per-table overrides such as custom PK and snapshot split column)

This is already established in MySQL-CDC and the shared CDC base config model. Using `table_list` here would introduce a third multi-table style and create confusion around parameter naming (for example `primary_keys` vs `primaryKeys`).

If we need a batch-style multi-table snapshot/incremental reader for Informix, it should continue to align with JDBC Source and use `table_list` there (separate from this CDC connector).

### Goals
- Align with existing CDC connector configuration patterns (`table-names`, `table-pattern`, `table-names-config`).
- Support snapshot + CDC with clear offset/checkpoint semantics.
- Improve read performance with Informix-specific optimizations when possible.

### Non-goals (for the initial version)
- Cover every Informix edition-specific CDC feature in one release.
- Replace JDBC Source for batch reads.

### Core Features

1. **Multi-Table Support (CDC-style)**
- Use `table-names` for explicit table lists.
- Use `table-pattern` for regex-based table selection.
- Use `table-names-config` for per-table overrides (for example `primaryKeys`, `snapshotSplitColumn`).

2. **Change Data Capture (CDC)**
- **Option A**: CDC API (Enterprise Edition), preferred for low latency.
- **Option B**: Log-based CDC (logical logs), for Standard Edition if feasible.
- **Option C**: Trigger-based CDC as a fallback.

3. **Type Mapping**
- Support Informix-specific types (for example, SERIAL8, LVARCHAR, Smart LOBs) beyond basic JDBC mappings.

4. **Performance Tuning**
- Fragmentation-aware and parallel reads where applicable.
- Standard connector tuning parameters such as `fetch_size`.

## Configuration Examples

### CDC (Multi-Table, `table-names` + `table-names-config`)

```hocon
env {
parallelism = 4
checkpoint.interval = 5000
}

source {
Informix-CDC {
# Connection
url = "jdbc:informix-sqli://informix-server.example.com:9088/stores_demo:INFORMIXSERVER=ol_informix"
username = "informix"
password = "******"

# Multi-table selection
table-names = ["stores_demo.customer", "stores_demo.orders", "stores_demo.items"]

# Per-table overrides (custom PK / snapshot split column)
table-names-config = [
{
table = "stores_demo.customer"
primaryKeys = ["customer_num"]
snapshotSplitColumn = "customer_num"
},
{
table = "stores_demo.orders"
primaryKeys = ["order_num"]
snapshotSplitColumn = "order_num"
}
]

# Startup mode (example naming; align with existing CDC connectors)
startup.mode = "initial"

fetch_size = 1000
}
}

sink {
Console {}
}
```

### CDC (Regex-based multi-table via `table-pattern`)

```hocon
source {
Informix-CDC {
# Connection omitted (same as above)
table-pattern = "stores_demo\\..*"
startup.mode = "initial"
}
}
```

## Technical Considerations
- **Configuration alignment**: Follow existing CDC connector patterns and the CDC base config model.
- **Table discovery**: Use a stable table identifier (for example `TableId`) to match `table-names-config` entries reliably.
- **Snapshot split strategy**: Use `snapshotSplitColumn` and align split semantics with CDC base.

Start by reviewing the existing MySQL-CDC patterns, the shared CDC base config model, and the JDBC Source behavior described in the issue. Determine which Informix CDC approach is feasible, then define support for table selection, per-table configuration, snapshot plus CDC offsets, and Informix-specific type mapping; done means the connector meets those goals with documented configuration and validation.

Written by the indexing model from the issue text.