Create a persistent variant of the drawer component

Nobody has claimed this yet.

### Summary

Create a persistent variant of the drawer component, i.e. which pushes content rather than overlaying it.

### 💬 Description

Currently, the drawer component appears above content, with an overlay / backdrop, when it is opened (usually called a "temporary" variant). It would be good if we also had a persistent variant, i.e. one that pushes content to the side, and that could remain open as the user switches between pages. This would be useful for multi-tasking and it would therefore be good for users dealing with complex apps.

See MUI's [persistent drawer variant](https://mui.com/material-ui/react-drawer/#persistent-drawer), vs. [their temporary variant](https://mui.com/material-ui/react-drawer/#temporary-drawer).

I would have created this variant while working on the original drawer ticket (#750) but there were no designs for this. E.g. where the drawer meets the content, would a border be displayed rather than a shadow? Should anything else look different?

I think it would also be good for a designer to decide on whether a persistent drawer should change to a temporary one as the screen size is reduced (and if so, at what size).

### 💰 User value

To allow users to keep the drawer open while interacting with the page content. It will help with multi-tasking and make it easier for users who need frequent access to the drawer's content

### 🚨 Urgency (low, medium or high)

Low

### Additional info

This is low urgency as it hasn't been specifically requested by customers

No implementation file, test, or entry point is named. Start by locating the existing drawer component and its tests, then review the linked MUI persistent and temporary variants; resolve the missing design decisions about borders, shadows, and responsive behavior before defining what completion means.

Written by the indexing model from the issue text.