Frontend: Add granular trait control for client-side SDKs

[khvn26]

Support the new allow_client_traits_in_evaluation environment-level field in the Environment settings UI.

The Environment settings UI should now include a section that allows to define a policy in regards to traits sent over by client-side SDKs:

• The existing allow_client_traits should be controlled by the "Persist" toggle.
• The new allow_client_traits_in_evaluation field should be controlled by "Use in evaluation" toggle.
• Disabling "Use in evaluation" should disable the "Persist" toggle.

Update the docs accordingly.