As a PNR user
I want to be able to retrieve immutable PNRs 
So that I can retrieve an existing PNR Record to see what names and addresses are specified

Given pnr_service.rs already exists and is used for creating, updating and getting mutable PNRs
When retrieving immutable PNRs
Then use get_pnr function in pnr_service.rs as an example for creating an get_immutable_pnr function
And only get the Resolver pointer (but not the Personal pointer) and the PNR zone chunk
And get the content of Resolver pointer to get the PNR zone chunk directly
And review create_immutable_pnr function to understand the relationship between the Resolver pointer and the PNR zone chunk

Given pnr_controller.rs already exists and is used for creating, updating and getting mutable PNRs
When retrieving immutable PNRs
Then use get_pnr function in pnr_controller.rs as an example for creating get_immutable_pnr
And return the same PnrZone struct as the body
And update lib.rs to add the endpoint where uploads_disabled is true
And use GET /anttp-0/pnr/immutable/{name} as the path

Implementation Notes

- Place any unit tests at the bottom of the same file as the associated production code
- Increment patch version of anttp package in Cargo.toml
- Create a copy of this issue description and save to /spec using the name of this issue as the filename (with lower underscore case, starting with the 5 char padded issue number, e.g. 00001_issue_title.txt)
- Update unit tests to validate the changes
- Update newman tests to reflect the changes
