Refactor/foreign assets as thin proxy #2199

Job	Run time
forkless-update-data	0s
canary	0s
collator-selection	0s
forkless-update-no-data	0s
governance	0s
try-runtime	0s
node-only-update	0s
codestyle / clippy	2m 20s
codestyle / yarn_eslint	1m 3s
codestyle / rustfmt	16s
xcm / Prepare execution matrix	26s
yarn-dev / opal	38m 8s
yarn-dev / sapphire	28m 7s
unit-test / develop	7m 36s
yarn-dev / quartz	38m 51s
yarn-dev / unique	26m 53s
xcm / opal	1m 24s
xcm / quartz	1m 24s
xcm / unique	1m 21s
	2h 27m 49s

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