Add ignore pattern before using unusedExports by default

Before doing https://github.com/import-js/eslint-plugin-import/issues/1324 We should have a `varsIgnorePattern` or similar. There is cases where you don't want to remove all unsued exports.
For example in some project when we have a custom library / DS we export the props from the component files. Though we do not want to ignore the files itself, only interface / type that end with `Props`

Start by reading the implementation and tests for the unusedExports rule, especially how exported variables are selected. Define the ignore-pattern behavior for names ending in Props without ignoring entire files, then add coverage showing those exports are preserved while other unused exports remain removable.

Written by the indexing model from the issue text.