feat(tauri) add Notifications API

[lucasfernog]

What kind of change does this PR introduce? (check at least one)

• Bugfix
• Feature
• New Binding Issue #___
• Code style update
• Refactor
• Build-related changes
• Other, please describe:

Does this PR introduce a breaking change? (check one)

• Yes. Issue #___
• No

The PR fulfills these requirements:

• It's submitted to the dev branch and not the master branch
• When resolving a specific issue, it's referenced in the PR's title (e.g. fix: #xxx[,#xxx], where "xxx" is the issue number)

If adding a new feature, the PR's description includes:

• A convincing reason for adding this feature (to avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it)

Other information:

[rajivshah3]

Just a heads-up: mac-notification-sys (used by notify-rust on macOS) uses the deprecated NSUserNotification API, which is deprecated after macOS 10.14 (see h4llow3En/mac-notification-sys#10)

[jbolda]

Also waiting on upstream PR for windows support: hoodie/notify-rust#68