Fix support for the GitLab Slack App

Created by: jgangemi

The current implementation does not support the json data structure returned from the PUT and GET operations.

Sample JSON from a GET call using:

curl -s -X GET --header "PRIVATE-TOKEN: <token>" https://gitlab.com/api/v4/projects/<project-id>/integrations/gitlab-slack-application

{
  "id": 12345,
  "title": "GitLab for Slack app",
  "slug": "gitlab-slack-application",
  "created_at": "2024-10-15T01:57:19.376Z",
  "updated_at": "2024-10-15T13:28:48.228Z",
  "active": true,
  "commit_events": false,
  "push_events": false,
  "issues_events": false,
  "incident_events": false,
  "alert_events": true,
  "confidential_issues_events": false,
  "merge_requests_events": false,
  "tag_push_events": false,
  "deployment_events": false,
  "note_events": false,
  "confidential_note_events": false,
  "pipeline_events": false,
  "wiki_page_events": false,
  "job_events": false,
  "comment_on_event_enabled": true,
  "inherited": false,
  "vulnerability_events": false,
  "properties": {
    "channel": null,
    "notify_only_broken_pipelines": true,
    "branches_to_be_notified": "default",
    "labels_to_be_notified": "",
    "labels_to_be_notified_behavior": "match_any",
    "push_channel": "",
    "issue_channel": "",
    "confidential_issue_channel": "",
    "merge_request_channel": "",
    "note_channel": "",
    "confidential_note_channel": "",
    "tag_push_channel": "",
    "pipeline_channel": "",
    "wiki_page_channel": "",
    "deployment_channel": "",
    "incident_channel": "",
    "vulnerability_channel": "",
    "alert_channel": ""
  }
}

All of the boolean values aside from notify_only_broken_pipelines are already defined on the Service struct. the current SlackApplicationProperties just redeclares all the boolean properties and the SetSlackApplicationOptions doesn't declare almost all of what's in the properties attribute.