assetPrefix field missing in typescript

[tonyhallett]

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 interface for gatsby config is missing the assetPrefix

Reproduction Link

gatsby/packages/gatsby/src/redux/types.ts

Line 95 in 8dbf550

mapping?: Record<string, string>

Steps to Reproduce

1. Try to use the missing field in typescript

...

Expected Result

For it to be in the typescript definitions.

Actual Result

It is not in the typescript definitions

Environment

System:
    OS: Windows 10 10.0.19042
    CPU: (8) x64 Intel(R) Core(TM) i7-1065G7 CPU @ 1.30GHz
  Binaries:
    Node: 16.7.0 - C:\Program Files\nodejs\node.EXE
    Yarn: 1.21.0 - C:\Program Files\nodejs\yarn.CMD
    npm: 7.21.0 - C:\Program Files\nodejs\npm.CMD
  Browsers:
    Edge: Spartan (44.19041.1266.0), Chromium (94.0.992.50)
  npmGlobalPackages:
    gatsby-cli: 3.14.0
    gatsby-dev-cli: 3.14.0

Config Flags

No response