Add Sentry BreadcrumbHandler support

[HypeMC]

Adds support for getsentry/sentry-php#1199.

monolog:
  handlers:
    sentry:
      type: sentry
      hub_id: Sentry\State\HubInterface
      level: !php/const Monolog\Logger::ERROR
    sentry_breadcrumb:
      type: sentry_breadcrumb
      sentry_handler: sentry
      level: !php/const Monolog\Logger::INFO

# or if you don't have Sentry bundle installed

monolog:
  handlers:
    sentry:
      type: sentry
      dsn: "https://[email protected]/1"
      level: !php/const Monolog\Logger::ERROR
    sentry_breadcrumb:
      type: sentry_breadcrumb
      sentry_handler: sentry
      level: !php/const Monolog\Logger::INFO

Initially, I considered using the existing handler option instead of introducing the new sentry_handler option. However, I decided against it because the PSR logger doesn't get auto-enabled when the handler option is used:

monolog-bundle/DependencyInjection/MonologExtension.php

Lines 179 to 183 in ed0e4a2

	if (null === $handler['process_psr_3_messages']['enabled']) {
	$handler['process_psr_3_messages']['enabled'] = !isset($handler['handler']) && !$handler['members'];
	}

[HypeMC]

Taken from #514, should be merged first.