Add option to leave kernel sessions running when Positron is closed #1191

Job	Run time
Check Python types	3m 43s
Lint	1m 44s
Python Tests (ubuntu-latest, 3.8)	1m 42s
Python Tests (ubuntu-latest, 3.12)	1m 41s
Test Positron IPyKernel (macos-latest, 3.9)	2m 0s
Test Positron IPyKernel (windows-latest, 3.10)	6m 16s
Test Minimum Positron IPyKernel Dependencies (ubuntu-latest, 3.8)	3m 22s
Test Positron IPyKernel (ubuntu-latest, 3.11)	2m 48s
Test Positron IPyKernel (ubuntu-latest, 3.12)	3m 21s
Test TypeScript (ubuntu-latest, 3.x, ts-unit)	3m 4s
Test TypeScript (ubuntu-latest, 3.x, functional)	1m 59s
Test TypeScript (macos-latest, 3.x, ts-unit)	2m 49s
Test TypeScript (macos-latest, 3.x, venv)	3m 20s
Test TypeScript (macos-latest, 3.x, single-workspace)	3m 45s
Test TypeScript (macos-latest, 3.x, debugger)	2m 10s
Test TypeScript (macos-latest, 3.x, functional)	1m 39s
Test TypeScript (macos-latest, 3.x, smoke)	3m 55s
Test TypeScript (windows-latest, 3.x, ts-unit)	5m 48s
Test TypeScript (windows-latest, 3.x, functional)	4m 48s
	59m 54s

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