Consideration of Enum Placement and Versioning Strategy for Future Upgrades

[coderabbitai]

This issue is to consider the placement of enums and the versioning strategy for future upgrades of the ClientChainGateway and ExocoreGateway contracts. This is a consideration for later and does not need to be resolved immediately as the contracts are not yet in production. For more details, see the discussion in PR #24: #24