RelayChainAccountId32Aliases

[xlc]

Add RelayChainAccountId32Aliases to xcm-support.

Similar to AccountId32Aliases from Polkadot, but also accept AccountId32 from relaychain.

Need to make sure not accepting AccountId32 from other parachains.

Need integration tests.

[zqhxuyuan]

• first stage: add RelayChainAccountId32Aliases struct, and add unit-testcase: relay account and tests #651
• second stage: add integration test

[zqhxuyuan]

I've checked homa_lite config, and found type SovereignSubAccountLocation use create_x2_parachain_multilocation() which make form of (1, X1(AccountId)) , and it's like RelayChainAccountId32Aliases we add here to xcm-support. right? @xlc @syan095

[xlc]

RelayChainSovereignSubAccount represents a sub account of Karura sovereign account on relaychain. It is used to send KSM into this account to perform staking.