HIP-745: Optionally send transaction data without required transaction fields

### Problem

**Summary**

It should be possible to serialise a transaction without freezing it and in addition, it should be possible to serialise an incomplete transaction (e.g. missing node_account_id and transaction_id as a minimum, maybe others). It should also be possible to add signatures to a transaction without freezing it.

HIP: [745](https://hips.hedera.com/hip/hip-745)

### Solution

- [ ] Design the feature
- [ ] Feedback on feature design
- [ ] Define example for feature
- [ ] Merge design to references repo
- [ ] Schedule to update Java/JS/Go/Swift/Rust/C++

### Alternatives

_No response_