[Enhancement] Generate documentation should warn about syncing a secret in an Excluded namespace

[eitah]

Description

https://kyverno.io/docs/writing-policies/generate/#clone-examples does not mention that excluded namespaces for clone secrets are unable to sync properly. This is an issue because we copied the sync secrets policy expecting that the match and exclude blocks were unrelated to the clone fields. In fact, the clone needs to be in an allowed namespace for the trigger in order for the sync feature to work.

Stemming from bug report here: https://github.com/kyverno/policies/issues/1056

Slack discussion

https://github.com/kyverno/policies/issues/1056