Added: API endpoint to trigger a user email notification with their assigned assets

[lukasfehling]

Description

To automatically notify our active users we need to trigger the notification email with all their assigned assets via a api request. I just added the same functionality that is already existing in the GUI to the api functionality.

Type of change

• New feature (non-breaking change which adds functionality)
• This change requires a documentation update

How Has This Been Tested?

• Tested the endpoint locally with different user ids

Test Configuration:

• PHP version: 8.1.11
• MySQL version: 8.0.27
• Webserver version: Laravel Valet 3.1.9

Checklist:

• I have read the Contributing documentation available here: https://snipe-it.readme.io/docs/contributing-overview
• I have formatted this PR according to the project guidelines: https://snipe-it.readme.io/docs/contributing-overview#pull-request-guidelines
• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[what-the-diff]

• Added a new route to the API
• Added a method in UsersController that sends an email with all assigned assets of this user

[lukasfehling]

@snipe sorry... Second try

[snipe]

Looks great, thanks!

[welcome]

Congrats on merging your first pull request! 🎉🎉🎉