[MialLewis]

This PR adds facility and exit code fields to the slack notification.

• Facility, so we don't have to infer facility from the email address, this is sometimes ambiguous.
• Exit code, I've added functionality to make this more informative.

Payload to slack api after this change:

{
  "channel": "#error-reports",
  "username": "Error Reporter",
  "text": "\nName: Mial Email: mial.lewis@stfc.ac.uk\nFacility: ISIS\nAdditional text:\ntest123\nUsing: mantidworkbench 6.16.20260929.1355.dev3 on macOS 26.7\nIssue link: \nExit code: -11 (SIGSEGV)\nStack Trace:\n",
  "icon_emoji": ":sadmantid:",
  "attachments": [
    {
      "mrkdwn_in": [
        "text"
      ],
      "text": "```Not provided```"
    }
  ]
}

To test, if you want, deploy a local test instance and check the payload yourself.

[MohamedAlmaki]

LGTM