title: Setting environment variables of Sentry dynamically for logback.xml Sentry appender
body: <p>My app is using slf4j and naturally, I have a logback.xml file. I try to add a Sentry appender to this file. This is my logback.xml file.</p>
  
  <pre class="lang-xml prettyprint-override"><code>&lt;appender name="CONSOLE-INFO" class="ch.qos.logback.core.ConsoleAppender"&gt;
          &lt;filter class="ch.qos.logback.classic.filter.LevelFilter"&gt;
              &lt;level&gt;INFO&lt;/level&gt;
              &lt;onMatch&gt;ACCEPT&lt;/onMatch&gt;
              &lt;onMismatch&gt;DENY&lt;/onMismatch&gt;
          &lt;/filter&gt;
          &lt;target&gt;System.out&lt;/target&gt;
          &lt;encoder&gt;
              &lt;pattern&gt;%d %p %c{1.} %m%n&lt;/pattern&gt;
          &lt;/encoder&gt;
      &lt;/appender&gt;
      &lt;appender name="CONSOLE-ERROR" class="ch.qos.logback.core.ConsoleAppender"&gt;
          &lt;filter class="ch.qos.logback.classic.filter.LevelFilter"&gt;
              &lt;level&gt;ERROR&lt;/level&gt;
              &lt;onMatch&gt;ACCEPT&lt;/onMatch&gt;
              &lt;onMismatch&gt;DENY&lt;/onMismatch&gt;
          &lt;/filter&gt;
          &lt;target&gt;System.error&lt;/target&gt;
          &lt;encoder&gt;
              &lt;pattern&gt;%d %p %c{1.} %m%n%ex{100}&lt;/pattern&gt;
          &lt;/encoder&gt;
      &lt;/appender&gt;
      &lt;appender name="SENTRY" class="io.sentry.logback.SentryAppender"&gt;
          &lt;dsn&gt;
              https://...Sentry dsn
          &lt;/dsn&gt;
          &lt;filter class="ch.qos.logback.classic.filter.ThresholdFilter"&gt;
              &lt;level&gt;ERROR&lt;/level&gt;
          &lt;/filter&gt;
          &lt;encoder&gt;
              &lt;pattern&gt;%d %p %c{1.} %m%n%ex{100}&lt;/pattern&gt;
          &lt;/encoder&gt;
      &lt;/appender&gt;
      &lt;logger name="kafkaOrderLogger" level="info" additivity="false"&gt;
          &lt;appender-ref ref="CONSOLE-INFO"/&gt;
      &lt;/logger&gt;
      &lt;logger name="kafkaOrderErrorLogger" level="error" additivity="false"&gt;
          &lt;appender-ref ref="CONSOLE-ERROR"/&gt;
      &lt;/logger&gt;
      &lt;logger&gt;
          &lt;appender-ref ref="SENTRY"/&gt;
      &lt;/logger&gt;
  
      &lt;root level="info"&gt;
          &lt;appender-ref ref="CONSOLE-INFO"/&gt;
          &lt;appender-ref ref="CONSOLE-ERROR"/&gt;
          &lt;appender-ref ref="SENTRY"/&gt;
      &lt;/root&gt;
  </code></pre>
  
  <p>My app is dockerized before deployment and as part of our ci/cd it is deployed on three different environment, staging pre and production.
  The problem is I can provide variables only through a property file at the root of my application. This property file will be filled with values based on the deployment environment This means I cannot have a sentry.properties in the resource folder that is filled automatically. What I want is to have Sentry environment set and preferably without touching code as is the whole point of slf4j appenders.</p>