add support for k8s_container resource type

[suraj-qlogic]

When setting the k8s_container resource type in logbak.xml,it doesn't fill in any of the resource labels associated with it.

logback.xml

<configuration>
    <appender name="CLOUD" class="com.google.cloud.logging.logback.LoggingAppender">
        <!-- Optional : filter logs at or above a level -->
        <filter class="ch.qos.logback.classic.filter.ThresholdFilter">
            <level>INFO</level>
        </filter>
        <log>my-log-test</log> <!-- Optional : default java.log -->
        <resourceType>k8s_container</resourceType>
        <flushLevel>WARN</flushLevel> <!-- Optional : default ERROR -->
    </appender>
    <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
        <encoder>
            <pattern>%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n</pattern>
        </encoder>
    </appender>
    <root level="debug">
        <appender-ref ref="CLOUD"/>
        <appender-ref ref="STDOUT"/>
    </root>
</configuration>

output:

resource: {
  type: "k8s_container"
  labels: {
    cluster_name: ""
    pod_name: ""
    container_name: ""
    namespace_name: ""
    location: ""
    project_id: "XXX"
   }
}

[Red-C]

Hi! thanks for merging the pr and supporting the k8s_container. the container name is still incorrect in our logs. what's the consideration of using prefix of hostname as the container name?