cleanup: refactor deeply nested if statement in vault_tokens.go
cleanup: refactor deeply nested if statement in vault_tokens.go

Refactored deeply nested if statement in vault_tokens.go to
reduce cognitive complexity by adding fetchTenantConfig function.

Signed-off-by: Rakshith R <2c7b05ed1488c7110901626c2c56645675e22767@redhat.com>

ceph/ceph-csi,ceph/ceph-csi,ceph/ceph-csi,ceph/ceph-csi