Feature request: Add support for server metadata in RollbarAppender XML configuration

Start at the RollbarAppender entry point and compare its XML-configurable properties with the Java ConfigBuilder server metadata example. Verify how the server host and metadata should be represented in XML, then confirm that a configured RollbarAppender passes both values through when logging.

Currently adding server metadata is only possible using java configuration example:

new ConfigBuilder.withAccessToken(accessToken)
                .environment(hostConfiguration.getEnvironment())
                .handleUncaughtErrors(true)
                .truncateLargePayloads(true)
                .language("java")
                .framework("spring")
                .server(() -> new Server.Builder()
                        .host(hostConfiguration.getHostId().getValue())
                        .metadata(Map.of(
                                "world", hostConfiguration.getWorld(),
                                "accountId", hostConfiguration.getAccountId()))
                        .build())
                .codeVersion(gitProperties.getShortCommitId())
                .build();

It would be nice if it was possible to add the server metadata from XML configuration in RollbarAppender for logback.

<appender name="rollbar-sync" class="com.rollbar.logback.RollbarAppender">
    <filter class="ch.qos.logback.classic.filter.ThresholdFilter">
        <level>${rollbar.level}</level>
    </filter>
    <accessToken>${rollbar.api-key}</accessToken>
    <codeVersion>@git.commit.id@</codeVersion>
    <enabled>${rollbar.enabled}</enabled>
    <environment>${environment}</environment>
    <framework>spring-boot</framework>
    <language>java</language>
    <server>
        <host>${host-id}</host>
        <metadata>
            <account>${accountId}</account>
            <wrold>${world}</wrold>
        </metadata>
    </server>
</appender>