As a PNR user
I want to be able to create immutable PNRs that map to 
So that I can have a globally resolvable name to data that cannot change

Given immutable PNR records must not be mutable
When adding an immutable PNR
Then there should only be 1 (resolver) pointer and 1 (IPNR zone) chunk
And the immutable PNR zone must only include immutable XOR addresses in the 'address' field 
And the logic for immutable PNR is as follows: Resolver Pointer (immutable) -> Chunk (PNR zone, with immutable addresses only) -> Immutable address
And the immutable PNR JSON body must be the same as mutable PNR (using PnrZone struct) 

Given pnr_service.rs already exists and is used for creating, updating and getting mutable PNRs
When creating immutable PNRs
Then use create_pnr function in pnr_service.rs as an example for creating an create_immutable_pnr
And only create the Resolver pointer (but not the Personal pointer) and the PNR zone chunk 
And point the Resolver pointer to the PNR zone chunk directly
And as the Resolver pointer has counter set to u64::MAX, it is immutable to changes

Given pnr_controller.rs already exists and is used for creating, updating and getting mutable PNRs
When creating immutable PNRs
Then use post_pnr function in pnr_controller.rs as an example for creating post_immutable_pnr
And use the same PnrZone struct as the body
And update lib.rs to add the endpoint where uploads_disabled is false
And use /anttp-0/pnr/immutable as the path

Given immutable PNRs cannot be changed
When defining endpoints for immutable PNRs
Then only POST and GET will be supported (as PUT/PATCH are for mutable data only)

Given PNR zones should only resolve to immutable addresses
When creating an immutable PNR
Then all address values in PnrRecords must be immutable addresses
And immutable addresses are hex strings that are exactly 64 characters long
And ChunkAddress::from_hex can validate they are valid

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
