Allow to configure globalHubMode for SentryAppender from logback.xml

[marbon87]

Problem Statement

We have a java swing app, that uses logback for logging and the SentryAppender from sentry-logback.
Sentry is configured in the logback.xml.

We need to enable globalHubMode, to get breadcrumbs across multiple threads. I didn't find a way to enable globalHubMode by using logback.xml. Only solution i found is to copy the content from SentryAppender#start()

Solution Brainstorm

Add the attribute globalHubMode in SentryAppender to get the possibilit of configuring globalHubMode from logback.xml

[adinauer]

Hey @marbon87 we only provide a subset of config options directly via the XML config. The intended way for more complex config is to use sentry.properties (ExternalOptions) but it seems globalHubMode also isn't configurable there yet. We can add it so it's read from sentry.properties. The way this will work is shown in our logback sample.