Fix/dashboard sigint exit

[cuishuang]

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | N/A (no issue filed)
| License       | AGPL-3.0
| Doc PR        | N/A



`pm2 dashboard` crashes when the user presses Ctrl-C.

The SIGINT handler is registered with a regular function. When the signal is emitted, `this` refers to the `process` object rather than the PM2 CLI instance. As a result, `this.Client` resolves to `process.Client`, which does not exist.



Use the already captured CLI instance, `that`, when disconnecting the PM2 bus during SIGINT handling.

This allows the dashboard to disconnect cleanly and exit with status code 0.

[CLAassistant]

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