instead of v3.0.0-000101010000000-00000000000,
that might be misleading as we don't develop etcd v3.0.0 any longer.
This version is a virtual version and is not supposed to be tagged
within the repository. We should tag real versions like: 3.5.0-alpha.0.
Please notice that go.etcd.io/etcd/client/v2 will be versioned as `v2.305.0-pre`.
The reason is that client v2 must have v2 version. I propose a
convention to envode the major version as 100x in minor version to make
the association to the underlying repository clear, staying within v2
version family.
The change was generated using:
```
DRY_RUN=false TARGET_VERSION="v3.5.0-pre" ./scripts/release_mod.sh update_versions
```
We make v2 client code a module go.etcd.io/etcd/client/v2.
Pretty mechanical change that can be summarized as:
mkdir client/v2
cd client/v2 && git mod init go.etcd.io/etcd/client/v2
git mv client/*.go client/v2/
find -name '*.go' | xargs sed -i --follow-symlinks 's|/v3/client["]|/client/v2\"|g'
+ fixing changelog, bom, go.mod etc.
