Improvements to childbounties IDs

[anaelleparity]

Issue originally erroneously logged here: polkadot-js/apps#9735

Current behavior
At the moment, curators have to manually check for childbounties IDs before and while creating/awarding a childbounty on Polkadot-JS apps, which has 2 implications:

-Curators are always indirectly competing with each other when using childbounties IDs in their calls
-Curators are always at risk of having complex time-consuming calls get rejected at the last minute

Some comments/suggestions
The current childbounties IDs system is suitable for a setup with 1 or 2 bounties, but very inefficient when there are 8+ bounties, as is the case on Polkadot at the moment.

-Could childbounties IDs be tied to their parent bountyID, rather than be shared across all bounties?
-Having a separate system for Childbounties IDs tied to their parent bounty ID would help curators and the community gain a better overview of childbounties-related data (i.e how many, for which bounty, how often, recurrent implementers profiles/recurring beneficiaries, etc.)

Thanks.