Make indexbuild macos QoS 'utility' by default

[AngelaGuardia]

What changed?

• Adds startup flag to set index builds MacOS QoS to utility by default

Why did it change?

• Developers have reported excessive battery usage related to background indexing

How is it tested?

• Added debug statements to the bazel_build.sh to see the startup flag being added for index builds
• I was unable to directly confirm (via my macbook) that the java process was actually set to utility - open to suggestions on how to do this.

[thiagohmcruz]

cc @brentleyjones, thoughts on this change? Also, I can't see build results when clicking on the links to jobs here, is it because of it's based on @AngelaGuardia's fork?

Last, @AngelaGuardia I believe you'd have to update fixtures too in this PR.

[AngelaGuardia]

Tried confirming that this change actually changes the qos of the bazel process by using this command sudo powermetrics --show-process-qos --show-process-qos-tiers --show-cpu-qos --samplers tasks -n 1 but I still don't see concrete proof that the flag actually changes the qos