Add dedicated execution API route for retrieving the large literal payload when TI start

### Body

- related: https://github.com/apache/airflow/pull/71871
- This is unnecessary in the first place since _most_ of the literal payload passing across language should be small enough and shouldn't be a large startup overhead.
- Create as a issue to keep track of this optional follow-up, it's only necessary until user complain.
- We can make it somehow _stream_ the value properly from serialized Dag payload to the Lang SDK runtime.

### Committer

- [x] I acknowledge that I am a maintainer/committer of the Apache Airflow project.