Implement mapping for UpdateGlobalNftLimit proposal type

[zeeshanakram3]

Context

Discovered while working on #4842

In the ProposalCreated mappings, the condition for checking proposalDetails.type === "UpdateGlobalNftLimit" does not exist. And since the ProposalCreated mappings throw an error for unimplemented/unsupported proposal types, this mapping would throw an exception when the UpdateGlobalNftLimit proposal type is unfiltered (in future runtime upgrade) and a proposal is created of this type.

joystream/query-node/mappings/src/proposals.ts

Line 306 in d144823

throw new Error(`Unspported proposal details type: ${proposalDetails.type}`)

Fix

Handle the UpdateGlobalNftLimit proposal type in the mapping