Store first session's expiry and roles

[kimlisa]

part of gravitational/teleport#4937

TODO: fix tests

Description

• Store first session's expiration and roles in local storage. This allows user to switchback to their default roles, and session lives for the remainder of the expiration
• After user assumes, or particularly when user switches back to lesser priveledged role, all opened tabs needs to be refreshed to apply new permission
• Moved BearerToken class/type to session.ts from localstorage.ts
• Placed a class name for Main component, so that I can target the styling for banner from one location