[Docs] Add link to suppressions chart for suppressing TypeSpec Linter errors

The chart at https://eng.ms/docs/products/azure-developer-experience/design/specs-pr-guides/pr-suppressions claims that "Permanent Suppressions" for check "TypeSpec Validation" are "Not possible". This is true for the TypeSpec Validation check itself.

However, TypeSpecValidation calls `tsp compile` which calls the TypeSpec Linter, and there **are** ways to suppress TypeSpec Linter rules. We should update the suppressions page to clarify that **some** parts of TypeSpecValidation are suppressable.