feat(toast): Add toast and error page for API error handling in the frontend

[joeherm]

This PR fixes MPP-4420.

How to test:

• l10n changes have been submitted to the l10n repository, if any.
• I've added a unit test to test for potential regressions of this bug.
• I've added or updated relevant docs in the docs/ directory.
• All UI revisions follow the coding standards, and use Protocol / Nebula colors where applicable (see /frontend/src/styles/colors.scss).
• Commits in this PR are minimal and have descriptive commit messages.

Description

• Adds a toast when we receive an error from API calls
• Adds basic error layout for /accounts/profile and /phone

Possible blockers / follow-up tickets

• Better design for error page
• Don't show errors for /runtime_data endpoint. We have defaults, maybe we don't care if the user knows about that endpoint erroring
• Don't show toast and page error at the same time

Screenshot (if applicable)

Screenshot when we get an error on a call after already loading some UI. For example, phone number suggestion:

Screenshot when we get an error for section where partial UI load isn't possible. For example, listing email addresses:

How to test

1. Pull the repo and build the frontend
2. Add a raise Exception("test") to RelayAddressViewSet.get_queryset
3. Attempt to load the email page in the browser

[joeherm]

I'm not sure why this is being added now 🤔