Add Slack badge to README banner

[Copilot]

📌 Description

Added Slack community badge to README banner, positioned after Discord badge. Links to https://milvus.io/slack.

✅ Changes

• Other (explain): Added Slack badge to README banner with for-the-badge style matching Discord badge

🔬 How to Test

1. View README.md to verify badge renders correctly
2. Confirm link redirects to https://milvus.io/slack

📝 Checklist

• Code compiles and runs
• Linting passes (Check jupyter notebooks: pip install "black[jupyter]" > black {file_or_directory})
• PR includes relevant docs or comments
• Rebased on the latest main (no merge commits or conflicts)

🧼 Commit Hygiene

✔️ Follow best practices:

• Small, focused commits with clear messages
• Group related changes together
• Avoid large monolithic commits
• Use meaningful commit messages (e.g., fix:, feat:, refactor:)

👀 Reviewer Notes

Single-line markdown change. Badge uses official Slack color (#4A154B) and shields.io logo integration.

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📎 Related Issues, PRs, or Docs

N/A

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Original prompt

submit a PR to add slack in readme banner redirecting to https://milvus.io/slack

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💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.

[sre-ci-robot]

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