On some pages we have a splitted layout for which we use `Primer::Alpha::Layout`, e.g.

* Meetings

* Storages


For the right side pane (called `Sidepanel`), I want a fixed component which can be re-used so that all right panes look the same

### Acceptance criteria

* Begin of the insertion[x]End of the insertion Begin of the deletion [ ]End of the deletion Create a Sidebar component
* Begin of the insertion[x]End of the insertion Begin of the deletion [ ]End of the deletion Provide slots for individual secions with
* Begin of the insertion[x]End of the insertion Begin of the deletion [ ]End of the deletion a header
* Begin of the insertion[x] a counter
* [x]End of the insertion Begin of the deletion [ ]End of the deletion an action button
* Begin of the insertion[x]End of the insertion Begin of the deletion [ ]End of the deletion some content Begin of the insertion
* [x] an optional footerEnd of the insertion
* Begin of the insertion[x]End of the insertion Begin of the deletion [ ]End of the deletion Use the `Primer::OpenProject::BorderGrid` internally

#### Hint for QA

* This will be implemented completely inside the primer\_view\_components repo, and this needs to be tested inside the lookbook (or in core after it was updated there, which will be probably be a separate ticket).