Add `purpose` field to device certificate #20358

Job	Run time
dispatch	5s
📊 Q&A	1m 11s
spelling / cspell	20s
docs	0s
rust / 🐧 Linux: 🦀 Rust tests	3m 23s
web / 🌐 Web tests	2m 16s
rust / 🍎 macOS: 🦀 Rust tests	3m 18s
python / (🐧 Linux only): 🐍 Python server tests	3m 29s
rust / 🏁 Windows: 🦀 Rust tests	3m 22s
⭐ CI is happy ⭐	1s
	17m 25s

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