No equivalent of --filter-affected for Terragrunt run-all stacks

Users running a single large Terragrunt stack with Use Run All enabled have no way to scope a run to the units affected by a change. Every triggered run executes terragrunt run-all across the entire project root regardless of what changed [https://docs.spacelift.io/vendors/terragrunt/run-all], which on a large project means long, wasteful runs and a single monolithic run log with no per-unit history.