feat(BottomSheet): Allow custom container/overlay in which to render the bottom sheet

#### Feature Description

Allow uses to customize where the bottom sheet is attached, other than the body.

#### Use Case

Single page web applications have many components, it would be nice to association the bottom sheet with specific components visually.

This is similar to https://github.com/angular/components/issues/7764. Both components define a viewContainerRef, however that does nothing in regards to bottom sheet placement with in the DOM.

Start by reading the Angular Material bottom-sheet implementation and its handling of viewContainerRef, then compare the placement requirements with the linked Angular components issue. Done means applications can choose a custom container and overlay instead of always attaching the bottom sheet to the body.

Written by the indexing model from the issue text.