Fix notifiers reading repo/branch from wrong source

[dc-larsen]

Summary

• Webhook, Slack, MS Teams, MS Sentinel, and SumoLogic notifiers read repository and branch from self.config, which never contains these fields, resulting in "Unknown" for both values in all outbound payloads
• The NotificationManager correctly populates these in the facts dict (manager.py:279-280), and the Jira notifier already reads from facts correctly
• Changed all five notifiers to read from facts instead of self.config

Test plan

• Verified self.config only contains init params (e.g. url), never repository/branch
• Verified facts dict contains correct repository and branch after NotificationManager.notify_all() populates them
• Tested WebhookNotifier, SlackNotifier, and SumoLogicNotifier with mock data, all return correct repo/branch
• Run Socket Basics scan with webhook enabled to confirm payload includes real repo/branch values

[lelia]

LGTM. Tested webhook functionality as follows:

• Created a dummy webhook at https://webhook.site
• Set value of INPUT_WEBHOOK_URL to point at my webhook in .env
• Ran socket-basics via Docker with the following args:

docker run --rm \
    --env-file .env \
    -v "$(pwd)":/workspace \
    socket-basics:1.0.28 \
    --workspace /workspace \
    --repo SocketDev/socket-basics \
    --branch fix/webhook-notifier-repo-branch \
    --javascript --secrets --trivy-vuln-enabled -v

• Confirmed webhook payloads now contain repository and branch values:

  "repository": "SocketDev/socket-basics",
  "branch": "fix/webhook-notifier-repo-branch",
  "scanner": "socket-security",

One future improvement to consider is adding a small unit test to verify notifiers prefer facts over self.config for repo/branch.