Changed plugins to rely on pipx + Added readme docs

[RobertoRoos]

I think the pipx injection is more robust if we're already installing Poetry with pipx.

And I copied the documentation style for options from https://github.com/actions/checkout

An example of usages: https://github.com/DEMCON/twincat-tools/actions/runs/13370258351

Relates to

• Error on Windows when requiring poetry plugin for Poetry 2.1.1 #89

[RobertoRoos]

An example with a run with multiple plugins: https://github.com/DEMCON/twincat-tools/actions/runs/13370735747

Using it like

    - name: Set up Poetry
      uses: RobertoRoos/actions-poetry@feature/plugins
      with:
        poetry-version: "2.1.1"
        poetry-plugins: "['poetry-dynamic-versioning[plugin]', 'poetry-plugin-bundle']"