[WIP] [Docs] Add conventions documentation #12519

Job	Run time
Build	3m 19s
Lint (rubocop)	1m 37s
Test (unit_models)	2m 38s
Lint (erblint)	1m 25s
Test (unit_services)	1m 24s
Lint (dfe_analytics)	54s
Deployment To Review	0s
Test (unit_forms)	1m 35s
Lint (yarn_lint_and_test)	1m 11s
Test (unit_components)	1m 9s
Test (unit_other)	1m 56s
Test (integration_auth)	1m 9s
Test (integration_find)	1m 25s
Test (integration_publish)	2m 17s
Test (integration_support)	1m 21s
Test (integration_other)	1m 11s
Parallel deployment before production	0s
Production deployment	0s
Sandbox deployment	0s
	24m 31s

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