Add external evaluation as a new access group rule

[Noanan]

Description

The new external evaluation access group rule has been added to the Access backend, this PR adds it here for additional support with the Cloudflare lib and terraform.

Has your change been tested?

Integration testing with terraform

Types of changes

What sort of change does your code introduce/modify?

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• [] I have updated the documentation accordingly.
• [] I have added tests to cover my changes.
• All new and existing tests passed.
• This change is using publicly documented (api.cloudflare.com or developers.cloudflare.com) and stable APIs.

[jacobbednarz]

looks good code wise; just waiting on the public API documentation and we can get this merged.

[jroyal]

Due to limitations in how the docs are generated on api.cloudflare.com we don't currently layout how these rules are created. Since its just a new rule type and there really isn't any new public documentation regarding a new api endpoint I think we will be ok. How the rule is defined is very unlikely to change at this point.

[jacobbednarz]

good enough for me! thanks for this @Noanan 👏