fix(docs): fix import commands

All resources are prefixed with zitadel_. Importing without this prefix doesn't work. This PR prepends the prefix in the import commands.

[ ] Short description of the feature/issue is added in the pr description
[ ] PR is linked to the corresponding user story
[ ] Acceptance criteria are met
[ ] All open todos and follow ups are defined in a new ticket and justified
[ ] Deviations from the acceptance criteria and design are agreed with the PO and documented.
[ ] No debug or dead code
[ ] My code has no repetitions
[ ] All non-functional requirements are met
[ ] The generic lifecycle acceptance test passes for affected resources.
[ ] Examples are up-to-date and meaningful. The provider version is incremented.
[ ] Docs are generated.
[ ] Code is generated where possible.

zitadel / terraform-provider-zitadel