Add class to manage Kafka REST Proxy

[i7c]

This patch adds a new class confluent::kafka::rest which can be used to
manage the Kafka REST Proxy as described here:
https://docs.confluent.io/current/kafka-rest/docs/intro.html

The class provides sane defaults to most parameters for and the
possibility to fine-tune the configuration with optional params.

[walkamongus]

Just FYI it looks like the class is missing the $logging_config parameter. Here is what it would look like using the default config from the 5.3 confluent-kafka-rest package:

  Hash[String, Variant[String, Integer, Boolean]] $logging_config = {
    'log4j.rootLogger'                               => 'INFO, stdout, file',
    'log4j.appender.stdout'                          => 'org.apache.log4j.ConsoleAppender',
    'log4j.appender.stdout.layout'                   => 'org.apache.log4j.PatternLayout',
    'log4j.appender.stdout.layout.ConversionPattern' => '[%d] %p %m (%c:%L)%n',
    'log4j.appender.file'                            => 'org.apache.log4j.RollingFileAppender',
    'log4j.appender.file.maxBackupIndex'             => '10',
    'log4j.appender.file.maxFileSize'                => '100MB',
    'log4j.appender.file.File'                       => '${kafka-rest.log.dir}/kafka-rest.log',
    'log4j.appender.file.layout'                     => 'org.apache.log4j.PatternLayout',
    'log4j.appender.file.layout.ConversionPattern'   => '[%d] %p %m (%c)%n',
  },

The docs also indicate a bootstrap_servers parameter, but this doesn't seem to be used in the code.