Allow additional account as container chain manager

[fgamundi]

Allows the container chain registrar creator to assign a separate account as the only valid manager for that chain in Tanssi.
On chain registration the manager will be set to the creator, and then only the creator can set a new manager.

[github-actions]

Coverage Report

(master)

@@                 Coverage Diff                  @@
##           master   fg-chain-manager      +/-   ##
====================================================
- Coverage   69.53%             69.46%   -0.07%     
  Files         221                221              
+ Lines       38452              38524      +72     
====================================================
+ Hits        26736              26760      +24     
+ Misses      11716              11764      +48     

Files Changed	Coverage
/pallets/registrar/src/lib.rs	90.07% (-0.57%)	🔽
/pallets/registrar/src/weights.rs	35.27% (-3.08%)	🔽
/runtime/common/src/migrations.rs	46.15% (-3.85%)	🔽

Coverage generated Tue May 21 11:24:03 UTC 2024

[girazoki]

merge master back in @fgamundi please!