[ibm-mq-metrics] Add slf4j backend

Running the jar gives:
```
SLF4J(W): No SLF4J providers were found.
SLF4J(W): Defaulting to no-operation (NOP) logger implementation
SLF4J(W): See https://www.slf4j.org/codes.html#noProviders for further details.
```

The shaded binary needs a slf4j backend. slf4j-simple would work.