gatsby-adapter-netlify not generating headers for redirects

[techfg]

Preliminary Checks

• This issue is not a duplicate. Before opening a new issue, please search existing issues: https://github.com/gatsbyjs/gatsby/issues
• This issue is not a question, feature request, RFC, or anything other than a bug report directly related to Gatsby. Please post those things in GitHub Discussions: https://github.com/gatsbyjs/gatsby/discussions

Description

The gatsby-adapter-netlify is not generating HTTP headers defined in gatsby-config if the route is a redirect route.

Redirect routes support headers as defined in IRedirectRoute.

Based on this comment this appears to be functionality that is not yet implemented but with no "stock" way to "opt-out" of the netlify adapter when building and running on Netlify, this should likely be addressed sooner than later.

Reproduction Link

https://codesandbox.io/p/sandbox/gatsby-adapter-netlify-redirect-headers-missing-82qlk9?file=%2Fpublic%2F_headers

Steps to Reproduce

1. Go to repro on codesandbox
2. View the public folder and open _headers file
3. There is no header for the path /testpage, however other headers from gatsby-config are present

To re-create the scenario:

1. Run clean task
2. Run build task
3. View _headers file in public folder

Expected Result

A X-PageName header should be defined in _headers for the route /testpage

/testpage/
  X-PageName: TestPage

Actual Result

The X-PageName header for /testpage is not in the _headers file.

Environment

System:
    OS: Linux 6.1 Debian GNU/Linux 11 (bullseye) 11 (bullseye)
    CPU: (2) x64 AMD EPYC
    Shell: 5.1.4 - /bin/bash
  Binaries:
    Node: 18.17.1 - ~/.local/state/fnm_multishells/2521_1694238260312/bin/node
    Yarn: 1.22.19 - /usr/local/bin/yarn
    npm: 9.6.7 - ~/.local/state/fnm_multishells/2521_1694238260312/bin/npm
  npmPackages:
    gatsby: ^5.8.1 => 5.12.4
    gatsby-adapter-netlify: ^1.0.0 => 1.0.0

Config Flags

N/A

[techfg]

Will defer to Gatsby team, but this can likely be closed in favor of #38542.