[Dashboard] Notifications Page

[gtsiolis]

Problem to solve

Currently, notifications settings are mixed with other user settings like Environment Variables, API Tokens, etc.

This is part of #3300. 🍕

User Experience goal

The user should be able to a navigate and update their notifications settings while the system confirms their action by showing a toast notification.

Proposal

In this first MVC (minimum viable change), we can do the following:

1. Introduce a dedicated notifications settings page.
2. Checking or unchecking the two existing options should trigger a toast notification at the bottom of the screen.

Components involved:

1. Checkbox
2. Toast

Designs

Notifications	Notifications (Spacing)

In the designs above, there're are also hover states for the top tabs and the sidebar tabs.

See also design specs.

Documentation

No documentation changes are needed for this first iteration.

[gtsiolis]

Closing as this has been resolved in #3513. Added a follow-up issue in #3530.