Granular plan / apply

[mwarkentin]

Currently plans / applies / locks are an all or nothing proposition.

Being able to plan / review / apply slices independently allows for safer operation during large changes.

Examples:

• modifying something in a root terragrunt file which means potential changes across dozens or hundreds of slices
• modifying something shared across multiple regions and being able to deploy them one at a time (eg. s4s -> st1 -> st2 .... de -> us)

[mwarkentin]

https://github.com/getsentry/ops/pull/10981#issuecomment-2168460887

23 slices with changes, comments are truncated (#195), so I need to click into all of the GHA plan actions and try to make sure I don't miss anything to feel confident to apply