Improved the explanation of "Enable Posture only mode".

### Existing documentation URL(s)

- https://developers.cloudflare.com/cloudflare-one/team-and-resources/devices/cloudflare-one-client/configure/modes/device-information-only/

### What changes are you suggesting?

The documentation states that client certificate provisioning needs to be enabled using the API, but this API token permission requires the use of a "User API Token," not an "Account API Token."

If mistakenly use an "Account API Token," the following error will be returned:
`{"result":null,"success":false,"errors":[{"code":1039,"message":"malformed actor email claim"}],"messages":[]}`
If use a "User API Token," the following success message will be returned:
`{"result":{"enabled":true},"success":true,"errors":[],"messages":[]}`
Explicitly stating this in the documentation will allow users to configure it correctly without confusion.

There has been a similar post in the community in the past:
https://community.cloudflare.com/t/undocumented-error-returning-from-api-calls/866382

### Additional information

_No response_