[macOS] Spotlight indexing causes performance issues

**Describe the bug**
On macOS, when Multipass spawns files (especially when downloading cloud images), CPU usages spikes. Prior investigation shows that `mds_stores` and `mediaanalysisd` hogging the CPU which seems to be resolved by disabling the Spotlight.

**Expected behavior**
No significant performance degradation when downloading images.

We should probably look into disabling Spotlight indexing for the Multipass data and cache directories.