Add new configuration flag for token exchange

[zzooeeyy]

For

• https://github.com/Shopify/develop-app-access/issues/147

What this PR does

• Add new configuration flag to enable token exchange workflow
• We'll need to rename wip_token_exchange configuration once it's ready to be used.

Checklist

Before submitting the PR, please consider if any of the following are needed:

• [NA] Update CHANGELOG.md if the changes would impact users
• [NA] Update README.md, if appropriate.
• [NA] Update any relevant pages in /docs, if necessary
• [NA] For security fixes, the Disclosure Policy must be followed.

[paulomarg]

Works for me, though I don't love the wip in the config name. Could we say unstable instead?

Also, I assume the actual functionality will come later? 😄

[zzooeeyy]

Works for me, though I don't love the wip in the config name. Could we say unstable instead?
Also, I assume the actual functionality will come later? 😄

Yes, actual functionality will come later, that's why I'm inclined to name it "wip" since it's actually "work in progress", "unstable" to me means something that's already implemented and it's partially working, just unstable..