[Feature Request] Infinite scroll for el-select component

### Existing Component
Yes

### Component Name
el-select

### Description
I would like to have an ability to enable infinite scrolling for el-select to be able to display a huge list of options using API.

Start by locating the el-select component entry point and reviewing how it currently renders and loads options. Define the interaction and API-loading behavior for a huge option list before deciding what implementation and coverage are needed; done means infinite scrolling can be enabled for el-select and reliably loads additional options.

Written by the indexing model from the issue text.