[Feature] Check for a new version and notify the admin(s)

[alexjustesen]

Description

This PR implements the system version checker and provides notifications to the admin user(s) when a new version of Speedtest Tracker is available.

Heavily inspired by how Ploi Roadmap handles version checking.

• closes Check for a new version and notify the admin(s) #977

Changelog

Added

• artisan about now reports the local version and if the local version is out of date.
• check for updates weekly and notify the admin user(s) if one is available via database notification

Changed

• use SystemChecker instead of config/speedtest.php to get the current version.

Screenshots

Update Available

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