Switch away from using npm for metro #5203

Job	Run time
Build Docker image	5m 25s
Build application and assets	5m 43s
file_changes	4s
Linting / TypeScript	1m 31s
Linting / Elixir	3m 56s
Formatting / JavaScript & TypeScript	1m 23s
Formatting / Elixir	3m 44s
Unit tests / JavaScript / Mocha	1m 28s
Unit tests / JavaScript & TypeScript / Jest	3m 6s
Linting / CSS	1m 27s
Linting / JavaScript	1m 21s
Type checks / Elixir	4m 17s
Type checks / TypeScript	1m 31s
Unit tests / Elixir / mix coveralls.html	59s
	35m 55s

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