Templates(select) - improve documentation around initial selections

The docs aren't clear about how to go about setting an initial selection for the different selects. It is the same pattern, and the examples use it (setting a selected prop on an option), but it would be helpful to explain this in the docs.

Also, currently you can still pass selected to the templates because the props tables extend SelectProps, but this is currently nonfunctional to a user since state is managed internally. My thought is we can exclude the prop from the extension, and potentially add an initialSelection prop as a more direct way of setting an initial selection (and an alternative to the option prop method that currently exists).

Jira Issue: PF-34

テンプレートのドキュメント、その select の例、および SelectProps を拡張している props テーブルを見つけます。まず、異なる select で既存の選択済みオプションのパターンがどのように説明されているかを比較します。初期選択の動作が明確にドキュメント化され、selected と考えられる initialSelection prop の API 上の扱いが解決され、一貫して反映されていれば完了です。