[Whitelisted Caller] Upgrade remaining system chains to 1.6.x, enable RFC-103 and fix XCM version subscriptions

The proposal aims to upgrade system chains to v1.6.1 along with two calls:

• enabling RFC-103, which makes Elastic Scaling safer by ensuring each parachain block is locked to a specific relay-chain core, preventing duplication and boosting performance
• Fixing XCM version subscriptions for some system chains

These are being bundled into one proposal to avoid multiple back-to-back whitelisted referenda. Hence, the Fellowship is also voting in parallel to whitelist the proposal hash. Further details can be found in the proposal post. If approved, it is scheduled to enact at block 29613600.