Release v12.1.0 tempest.lib interfaces

We have re-integrated tempest-lib code into tempest.lib under the tempest repository again.
Then we can release the tempest.lib as stable interfaces in the middle of releases.
This is the first tag only for releasing tempest.lib which contains
 - Image v1 clients
 - Image v2 clients
 - Identity v2 clients
 - Network router client
 - Add an argument chunked to post()/put() of rest_client
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