[feature] Add per-repo allowlist for direct-change attribute detection

[yushan8]

Summary

Intent:

• GetChangedTargets classifies a target as directly changed (distance 0)
  whenever its attribute set differs between revisions.
• Some Bazel attributes are pure BUILD-file bookkeeping (e.g.
  generator_location, which shifts whenever unrelated lines move earlier in
  the same file) rather than semantic configuration, so comparing the full
  attribute set can misclassify cosmetic churn as a direct change.

Changes:

• Add RepositoryConfig.DirectlyChangedAttributes, a per-repo allowlist of
  attribute names that count as evidence of a direct change.
• Wire config.RepositoryConfigProvider into controller.Params/controller so
  GetChangedTargets can look up the allowlist for a request's remote.
• Thread the resolved allowlist through compareTargetGraphs and toDiffGraph
  so only allowlisted attributes (or all attributes, when unset) are kept on
  each target before diffing.

Test Plan

• Added TestToDiffGraph_OnlyKeepsAllowlistedAttributes and
  TestDirectlyChangedAttributesFor covering the allowlist filtering and
  lookup logic.
• Updated existing compareTargetGraphs/toDiffGraph call sites for the new
  parameter.