Investigate custom runner for Zephyr job

[wmamills]

Look at a custom runner for the Zephyr job as it is outgrowing the stock runner.

Right now it works with the stock runner by deleting a bunch of stuff github adds to the image. This processes takes ~ 6 minutes.

If we used a custom runner we could:
A) specify a bigger disk
B) start with stock Ubuntu

The down side would be we would need to pay for each minute the runner uses. There are no free minutes for custom runners.

[github-actions]

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