As a Tarchive user
I want to create tarchives with an archive.tar.idx that includes the file XorName and blsttc signature
So that I can allow others to easily verify that I created

Given tarchive_service.rs needs to generate signatures from a blsttc private key
When adding capability to TarchiveService
Then add a dependency for AnttpConfig and ensure it is provided where TarchiveService is instantiated

Given a tarchive should include XorNames and blsttc signatures for each file in the archive
When creating the index using 'index' function in tarchive_service.rs
Then for each entry_result generate an XorName string using from_content
And also generate a blsttc signature by calling Signature::from_bytes with the XorName bytes as the message and AnttpConfig.app_private_key as the private key
And then output both values out, as hex strings, to the index entry, after size (separated by spaces)  

Given archive.rs already defines Archive and DataAddressOffset
When adding XorName and signature to tarchives
Then build_from_tar should be updated to get the XorName and Signature from the tar_index parts
And then DataAddressOffset.data_address should be assigned the XorName value
And DataAddressOffset.signature field should be added and populated with the (optional) blsttc signature

Given archive.rs already contains build_from_public_archive for building archives from public archives
When building an archive from a public archive
Then set signature to None

Given file_controller.rs already returns response headers for archive file requests
When creating response headers on responses
Then update update_full_content_response and update_partial_content_response to include a new a new 'x-data-signature' header containing the signature (from resolved_address.archive.get(resolved_address.filepath).signature, if it exists)

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