Don't add processor to all loggers if tags specify a channel or handler

[HypeMC]

Similar to symfony/symfony#61526.

When you add a custom processor to a specific channel or handler, it gets added to all channels because ProcessorInterface is registered for autoconfiguration.

Here's a simple example:

#[AsMonologProcessor('my_channel')]
final class MyProcessor implements ProcessorInterface
{
    public function __invoke(LogRecord $record) {}
}

You'd expect this processor to be registered only for my_channel, but due to autoconfiguration it's added to every channel.

The workaround is to disable autoconfiguration and add an explicit tag.

services:
    App\MyProcessor:
        autoconfigure: false
        tags:
            - monolog.processor: { channel: 'my_channel' }

This PR ensures a processor is not added to all channels when an explicit channel or handler is configured.

[HypeMC]

CI failure is false positive, trailing_comma_in_multiline is not supported in PHP 7.2.

Decided to put in in one line instead.

[GromNaN]

LGTM.
@HypeMC can you rebase the PR on 3.x?

[GromNaN]

Thank you @HypeMC.