Release v0.6.0

Add A3-Ultra support for cluster creation (#286)

* Implement a3 ultra for cluster create

Signed-off-by: Piotr Pawłowski <ppawl@google.com>

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Signed-off-by: Piotr Pawłowski <ppawl@google.com>
Co-authored-by: Farhad Sharabiani <sharabiani@google.com>

Add Pathways end-to-end tests to XPK build tests and nightly tests. (#…

…103)