user-agent-blocking-rules: update validation for mode field

[tamas-jozsa]

Description

After following up with Firewall Team, we have agreed, that whitelist mode is the least popular, and we should rather validate against block, challenge, js_challenge, managed_challenge.

These values are also correlating with the public API:
https://api.cloudflare.com/#user-agent-blocking-rules-create-a-user-agent-blocking-rule

And the Terraform Provider:
https://github.com/cloudflare/terraform-provider-cloudflare/blob/master/internal/provider/schema_cloudflare_user_agent_blocking_rules.go#L33

Has your change been tested?

Swapped the library locally and tested new validations.

Screenshots (if appropriate):

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.

[github-actions]

changelog detected ✅

[github-actions]

This functionality has been released in v0.51.0.

For further feature requests or bug reports with this functionality, please create a new GitHub issue following the template. Thank you!