Add upgrade test for helm chart

[liam-mackie]

This PR adds a test to upgrade the helm chart from 1.*.* to the current version of the helm chart in the repo.
The test will fail if the script task fails (even if the agent is actually fine after the upgrade) to prevent a failed upgrade task.
Most of the test was taken from the Tentacle integration tests (thanks @APErebus!), with minor modifications to run outside of the Tentacle repo.

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Latest commit: 2f78b35

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[APErebus]

Awesome stuff @liam-mackie!