Werk #12701: Add four columns to livestatus for Robotmk

Add four columns to the services table in order to read Robotmk logs. The columns are

• robotmk_last_log, the file content of the Robotmk log;
• robotmk_last_log_gz, the gzipped file content of the Robotmk log;
• robotmk_last_error_log, the file content of the Robotmk error log;
• robotmk_last_error_log_gz, the gzipped file content of the Robotmk error log.

The columns return the content of the files or the empty string if they are not present.

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