Automatic merge from submit-queue (batch tested with PRs 36352, 36538, 37976, 36374)

etcd3: have prefix always prepended

ref: #36290

Previously, the prefix behavior is "sometimes prefixing". If the prefix already exists for the resource path, it will ignore.
With this PR, we make sure that prefix is always prepended in etcd3 storage backend. See the discussion in #36290