Add missing .gitignores to better support --addon-only scenarios (no test app) #706

Job	Run time
Lint JS	18s
Tests (addon-location)	55s
Tests: Type Check	16s
[email protected] : defaults with npm	1m 36s
Tests (test-app-location)	56s
[email protected] : defaults with yarn	1m 14s
Tests (addon-only)	31s
[email protected] : defaults with pnpm	53s
[email protected] : typescript with npm	1m 48s
Tests (monorepo with npm)	1m 37s
[email protected] : defaults with npm	1m 41s
[email protected] : typescript with yarn	1m 25s
Tests (monorepo with yarn)	1m 16s
[email protected] : defaults with yarn	1m 18s
[email protected] : typescript with pnpm	53s
Tests (monorepo with pnpm)	54s
[email protected] : defaults with pnpm	48s
Tests (rollup-build)	1m 17s
Tests (declarations-configuration)	43s
	20m 19s

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