To be able to recover the parachain in case of failure during the migration to Polkadot, the manager account has to be unlocked.

 Schedule a majority-carries referendum to be tabled next once it is legal to schedule
 an external referendum.

 Unlike `external_propose`, blacklisting has no effect on this and it may replace a
 pre-scheduled `external_propose` call.

Problem Statement:
- The manager account needs to be unlocked in order to recover the parachain in case of failure during migration to Polkadot.

Significance:
- Unlocking the manager account is crucial for ensuring the successful recovery of the parachain in case of failure during migration.

Proposed Solution:
- Unlock the manager account to enable the recovery of the parachain in case of failure during migration.

Expected Outcomes:
- Successful recovery of the parachain in case of failure during migration, ensuring the stability and continuity of the system.

#18 Unlock parachain manager account