[suppressions] Add property "if" to scope suppressions

[mikeharder]

Similar to:

https://docs.github.com/en/actions/writing-workflows/workflow-syntax-for-github-actions#jobsjob_idif

Examples:

- tool: TypeSpecValidation
  rules: [FolderStructure]
  if: context === "all"

- tool: TypeSpecValidation
  rules: [FolderStructure]
  if: date > 2025-01-01

Perhaps the value of "if" could be evaluated using some language, maybe JS in a sandbox? Or an even simpler language provided by a library?