Refactor/foreign assets as thin proxy #2207

Job	Run time
canary	0s
forkless-update-data	0s
collator-selection	0s
forkless-update-no-data	0s
try-runtime	0s
node-only-update	0s
governance	0s
unit-test / develop	7m 42s
yarn-dev / opal	26m 11s
xcm / Prepare execution matrix	28s
yarn-dev / sapphire	29m 12s
yarn-dev / quartz	28m 36s
yarn-dev / unique	27m 46s
codestyle / clippy	3m 12s
codestyle / rustfmt	15s
codestyle / yarn_eslint	49s
xcm / opal	1h 20m 53s
xcm / quartz	2h 47m 29s
xcm / unique	2h 58m 41s
	9h 11m 14s

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