Allow just the workspace "name" instead of full path when using --workspace

[tomdee]

The current behavior (from https://knip.dev/features/monorepos-and-workspaces)

Lint a single workspace
Use the --workspace (or -W) argument to focus on a single workspace (and let Knip run faster). Example:

Terminal window
knip --workspace packages/my-lib

The desired behavior:

knip --workspace my-lib

i.e. drop the packages prefix.

This matches how npm (and I think yarn) work
e.g. this works in npm, even if my-lib is stored in packages

npm run --workspace my-lib <script-name>`