feat(metrics): add observable gauge for batch queue worker length (#2… #2796

Job	Run time
typecheck / typecheck	5m 52s
units / packages / 🧪 Unit Tests: Packages (1, 1)	7m 45s
units / webapp / 🧪 Unit Tests: Webapp (5, 8)	7m 18s
units / internal / 🧪 Unit Tests: Internal (7, 8)	4m 38s
units / webapp / 🧪 Unit Tests: Webapp (8, 8)	2m 18s
units / webapp / 🧪 Unit Tests: Webapp (1, 8)	5m 35s
units / internal / 🧪 Unit Tests: Internal (5, 8)	3m 40s
units / internal / 🧪 Unit Tests: Internal (6, 8)	4m 53s
units / webapp / 🧪 Unit Tests: Webapp (3, 8)	5m 35s
units / internal / 🧪 Unit Tests: Internal (4, 8)	4m 53s
units / webapp / 🧪 Unit Tests: Webapp (6, 8)	2m 13s
units / internal / 🧪 Unit Tests: Internal (1, 8)	5m 5s
units / internal / 🧪 Unit Tests: Internal (8, 8)	2m 23s
units / webapp / 🧪 Unit Tests: Webapp (4, 8)	3m 21s
units / webapp / 🧪 Unit Tests: Webapp (2, 8)	3m 45s
units / webapp / 🧪 Unit Tests: Webapp (7, 8)	5m 32s
units / internal / 🧪 Unit Tests: Internal (3, 8)	5m 34s
units / internal / 🧪 Unit Tests: Internal (2, 8)	4m 40s
units / internal / 📊 Merge Reports	53s
publish-worker-v4 / build (supervisor)	2m 45s
publish-worker / build (coordinator)	1m 42s
publish-worker / build (docker-provider)	1m 25s
publish-worker / build (kubernetes-provider)	59s
publish-webapp / publish	6m 53s
units / webapp / 📊 Merge Reports	51s
units / packages / 📊 Merge Reports	20s
	1h 40m 48s

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