Introduce pkg/etk, a new TUI framework. #1735

Job	Run time
Run checks	53s
Run benchmarks	1m 38s
Check relative links in website	17s
Run tests (emulated riscv64)	1m 27s
Run tests (emulated s390x)	1m 23s
Run tests (ubuntu, 1.23.x)	1m 39s
Run tests (macos, 1.23.x)	1m 42s
Run tests (windows, 1.23.x)	3m 55s
Run tests (ubuntu, 1.22.x)	1m 8s
Upload test coverage (linux)	5s
Upload test coverage (macos)	10s
Upload test coverage (windows)	10s
	14m 27s

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