fix(charts/alerts): unique plugin name; align slack config

[richardtief]

Description

Updating the charts to reflect changes to the plugin.

• Assigning a unique name for the alerts plugin in the demo namespace.
• Adapt the Slack route configuration to new structure

What type of PR is this? (check all applicable)

• 🍕 Feature
• [ x ] 🐛 Bug Fix
• 📝 Documentation Update
• 🎨 Style
• 🧑‍💻 Code Refactor
• 🔥 Performance Improvements
• ✅ Test
• 🤖 Build
• 🔁 CI
• 📦 Chore (Release)
• ⏩ Revert

Related Tickets & Documents

• Related Issue # (issue)
• Closes # (issue)
• Fixes # (issue)

Remove if not applicable

Added tests?

• 👍 yes
• [ x ] 🙅 no, because they aren't needed
• 🙋 no, because I need help
• Separate ticket for tests # (issue/pr)

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

Added to documentation?

• 📜 README.md
• 🤝 Documentation pages updated
• [ x ] 🙅 no documentation needed
• (if applicable) generated OpenAPI docs for CRD changes

Checklist

• [ x ] My code follows the style guidelines of this project
• [ x ] I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[IvoGoman]

The service endpoint used by the CronJob needs to be adjusted to match the new service name: https://github.com/cloudoperators/greenhouse/blob/main/charts/demo/values.yaml#L43