Support pipelineTriggers API for GitLab triggers in Job DSL

### What feature do you want to see added?

Currently, when defining Jenkins pipeline jobs using Job DSL, the GitLab plugin requires the deprecated syntax:

```
triggers {
gitlabPush {
buildOnMergeRequestEvents(true)
buildOnPushEvents(true)
enableCiSkip(true)
}
}

```

This generates deprecation warnings in Job DSL seed jobs:

Warning: triggers is deprecated

**Problem**:

Job DSL now prefers properties { pipelineTriggers { ... } } for defining triggers.

The GitLab plugin (v1.9.9) does not currently support this API.

Users are forced to continue using the deprecated syntax, creating warnings and reducing clarity.

**Impact**:

Seed job logs are noisy due to warnings.

Encourages continued use of deprecated DSL constructs.

Reduces maintainability and clarity of pipeline definitions.

**Proposed Solution / Feature Request:**

Add support for defining GitLab triggers using the modern pipelineTriggers block.

Example of the desired syntax:

```
properties {
pipelineTriggers {
triggers {
gitlabPush {
buildOnMergeRequestEvents(true)
buildOnPushEvents(true)
enableCiSkip(true)
}
}
}
}
```

**Benefits**:

Eliminates deprecation warnings in Job DSL scripts.

Aligns the GitLab plugin with modern Job DSL best practices.

Improves maintainability and readability of Jenkins pipelines.

**Environment:**

Jenkins version: 2.516.3

GitLab plugin version: 1.9.9

Job DSL plugin version: 1.93

### Upstream changes

_No response_

### Are you interested in contributing this feature?

_No response_