[java-logging] Getting execution-id / trace in background functions

**Is your feature request related to a problem? Please describe.**
Logs from background functions are missing `execution_id` labe

**Describe the solution you'd like**
All logs from Background function should have the label, so it's easier to debug.

**Describe alternatives you've considered**
I have tried manually adding the `execution_id`, but it's not available from the `context` parameter.

**Additional context**
It's basically the same thing as in nodejs repository, see [here](https://github.com/googleapis/nodejs-logging/issues/591)