Functions Java Runtime cannot log exceptions to log topic

**Is your enhancement request related to a problem? Please describe.**
When using `context.getLogger().error("error message", exception)`, only the `error message` appears in the log topic. It will be great to have the exception been logged as well.

**Describe the solution you'd like**
Let exception been formatted and append into the message in `logAppender`

Start in the Java Functions Runtime at the logAppender handling for context.getLogger().error(message, exception). Reproduce the call with an exception and inspect the resulting log topic entry. Done means the original error message and a formatted exception are both written to the log topic.

Written by the indexing model from the issue text.