Support Monolog 3.x

[drmmr763]

Laravel 10x requires Monolog 3.

This package has a depdency on Monolog 1x || 2x. Would appreciate trying to go to Monolog 3x for composer compatibility.

[drmmr763]

Actually I see 3x was supported and it was dropped.

Removed in .3.0
c94b554
https://github.com/app-insights-php/monolog-handler/releases/tag/0.3.0

Added in .2.3
7df9538
https://github.com/app-insights-php/monolog-handler/releases/tag/0.2.3

@norberttech any idea why this was done?