Allow changing default "master" branch name in Insomnia Sync

[d19dotca]

Filing on behalf of a customer who would like to be able to rename the "master" branch which is created by default for the Insomnia Sync feature to "main" instead. Ideally this would be open to having the ability to rename it anything they'd like.

[JC5]

Yes please. Having a branch named master in 2023 (2025!) feels very 1990s.