Missing implementation of SLF4J API

Some libraries (e.g. com.floragunn:codova) on the EliatraSuite classpath use SLF4J for logging. Unfortunately, ELiatraSuit misses the SLF4J implementation. This causes the following problems:

• Logs written by SLF4J will be never stored in the log file (or by other appended configured for Log4j2)
• Warn messages are visible during OpenSearch start time (SLF4J: No SLF4J providers were found.)

The problem should be solved by the usage of "Log4j 2 SLF4J Binding", please see https://logging.apache.org/log4j/2.x/log4j-slf4j-impl.html