ENABLE_GATSBY_REFRESH_ENDPOINT should be available to set in config.flags

[phil-lgr]

Preliminary Checks

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Description

I think it should be added to https://github.com/gatsbyjs/gatsby/blob/master/packages/gatsby/src/utils/flags.ts

so we have one place to manage flags

Reproduction Link

https://github.com/gatsbyjs/gatsby/blob/master/packages/gatsby/src/utils/flags.ts

Steps to Reproduce

1. Open gatsby-config.js
2. add ENABLE_GATSBY_REFRESH_ENDPOINT: true, or maybe it should be REFRESH_ENDPOINT: true,

Expected Result

The refresh endpoint should be enabled via standard Gatsby flags

Actual Result

We need to set ENABLE_GATSBY_REFRESH_ENDPOINT when running the CLI

Environment

System:
    OS: macOS 11.4
    CPU: (8) arm64 Apple M1
    Shell: 3.2.57 - /bin/bash
  Binaries:
    Node: 16.5.0 - /var/folders/z3/1b10ld5s49n70q3n77_6_qch0000gn/T/yarn--1626446434911-0.6160726936976746/node
    Yarn: 1.22.10 - /var/folders/z3/1b10ld5s49n70q3n77_6_qch0000gn/T/yarn--1626446434911-0.6160726936976746/yarn
    npm: 7.19.1 - ~/.nvm/versions/node/v16.5.0/bin/npm
  Languages:
    Python: 2.7.16 - /usr/bin/python
  Browsers:
    Chrome: 91.0.4472.114
    Safari: 14.1.1

Config Flags

No response

[LekoArts]

Hi!

I don't see any value in adding this to the flags are those are just a mechanism for us to let people test out things that at some point get built-in anyways. Always setting ENABLE_GATSBY_REFRESH_ENDPOINT to true is not desirable and should be done by the user.

[phil-lgr]

As a user I prefer to have all flags and env vars at the same place

[wardpeet]

Thank you but we're going to keep it as an env var without adding it to the flags.