Add version header

[Sytten]

For future compatibility, the library should start sending the header X-GitHub-Api-Version.

[XAMPPRocky]

Thank you for your issue! That sounds like a great first issue for anyone who is interested in contributing to octocrab.

[dmgorsky]

in proposed PR #819 I added a section to Cargo.toml:

[package.metadata.github-api]
set-headers = ["X-GitHub-Api-Version: 2022-11-28", ]

We can specify an array of necessary http headers there; through build.rs they are injected in lib.rs in form of

pub const _SET_HEADERS_MAP: [(&str, &str); 1] = [("X-GitHub-Api-Version", "2022-11-28")];

and can be used in build_request():

for kv in _SET_HEADERS_MAP {
            builder = builder.header(kv.0, kv.1);
        }

[dmgorsky]

The headers are now set in [package.metadata.github-api] section of Cargo.toml ✅