[epic] Notifications Panel

[damoodamoo]

Implement a notifications panel, using the Azure Portal notifications panel as a guide.

For this implementation - it will:

• Only track operations passed to it from other components
• NOT try to gather all running operations on startup
• Only track operations the current user has triggered

To do:

• Design + spike how this will interact with other components, likely via the Context API
• 'bell' icon in the top nav bar opens a slideout panel
• A card is rendered for each long running operation
• When an operation completes, a toast notification is fired
• Consolidate all the polling logic into this set of components
• When an operation is triggered elsewhere in the app, the Operation URL to poll will be passed to the notifications panel
• Get the polling frequency from config

Future: (moved to separate task)