Add `purpose` field to device certificate #20357

Job	Run time
dispatch	7s
📊 Q&A	1m 12s
spelling / cspell	31s
docs	0s
web / 🌐 Web tests	3m 4s
rust / 🐧 Linux: 🦀 Rust tests	4m 8s
rust / 🍎 macOS: 🦀 Rust tests	4m 12s
python / (🐧 Linux only): 🐍 Python server tests	3m 37s
rust / 🏁 Windows: 🦀 Rust tests	4m 1s
⭐ CI is happy ⭐	1s
	20m 53s

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