Introduce ScriptTrigger & CommandsTrigger for the PHP plugin

## Context

Part of #313. `plugin-scripts` wants every submodule to expose a `ScriptTrigger` and a `CommandsTrigger`, so a flow can be triggered whenever the underlying script/commands execution completes, with an **exit condition** deciding whether the trigger fires based on the result (e.g. only on failure).

`plugin-script-php` is missing both. Existing implementations in `plugin-script-go`, `plugin-script-node`, `plugin-script-python`, `plugin-script-ruby`, and `plugin-script-shell` (same package as the task classes, no nested subpackage) can be used as a reference.

## What to implement

### 1. `ScriptTrigger`

- Triggers when `io.kestra.plugin.scripts.php.Script` execution completes.
- Emits an event containing: command executed, arguments, env (if available), exit code, stdout/stderr (if capture enabled), and contextual metadata (execution id, namespace, flow id).

### 2. `CommandsTrigger`

- Triggers when `io.kestra.plugin.scripts.php.Commands` execution completes.
- Emits an event containing: commands executed (or the matched one), exit code(s), stdout/stderr if available, and contextual metadata (execution id, namespace, flow id).

## Trigger configuration requirements

Each trigger should accept at least:

- `commandPattern` (string / regex / glob)
- `argumentsPattern` (optional)
- `exitCondition` (string expression — can match on exit code, output, or a literal condition)

## Example YAML

```yaml
triggers:
- id: on_php_fail
type: io.kestra.plugin.scripts.php.ScriptTrigger
commandPattern: ".*"
exitCondition: "exitCode != 0"

triggers:
- id: on_php_commands
type: io.kestra.plugin.scripts.php.CommandsTrigger
commandPattern: ".*"
exitCondition: "exitCode == 0"
```

Start by comparing the existing trigger implementations in plugin-script-go, plugin-script-node, plugin-script-python, plugin-script-ruby, and plugin-script-shell. Add ScriptTrigger and CommandsTrigger for the PHP Script and Commands tasks, covering the requested command, arguments, environment, exit status, output, and contextual metadata fields. Done means both triggers support command and optional argument patterns plus exitCondition expressions for the example success and failure cases.

Written by the indexing model from the issue text.