## Description 

Adding a validator signature field to checkpoint 

## Test Plan 
Postman local call vs FN

![image](https://user-images.githubusercontent.com/123408603/228853281-548b56c1-f09b-426f-8648-27794da07d7b.png)

Indexer + FN signatures match for a single checkpoint

![image](https://user-images.githubusercontent.com/123408603/228853969-9b5733e3-5ddf-4abd-a15e-12bf96fdcb7e.png)

Indexer call:

![image](https://user-images.githubusercontent.com/123408603/228859487-9e680616-b140-4b40-b99c-06df3cf9bfed.png)

---
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### Type of Change (Check all that apply)

- [ ] user-visible impact
- [ ] breaking change for a client SDKs
- [ ] breaking change for FNs (FN binary must upgrade)
- [ ] breaking change for validators or node operators (must upgrade
binaries)
- [ ] breaking change for on-chain data layout
- [ ] necessitate either a data wipe or data migration

### Release notes