ISSUE-18532: [Enhancement] Support reading config options from file in Function Java Runner (JavaInstanceStarter)

[sijie]

Original Issue: apache#18532

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• I searched in the issues and found nothing similar.

Motivation

Currently the JavaInstanceStarter uses JCommander to parse command line args. However in certain cases reading from command line is not very flexible (think we need to use a env var as an argument but the container has no shell access). Thus we need to support reading configs from a file.

This is necessary for :

• update replicas will cause all pods been rescheduled function-mesh#368
• Build distroless package for better security, smaller size, speed and more function-mesh#448

BTW, we can provide a new issue for python as well.

Solution

Solution:

• add a new command line flag "--config_file" and accepts a file URl
• read the file using PulsarConfigurationLoader and create a new class JavaInstanceConfiguration extends PulsarConfiguration.
• Config priority : command line > conf file.
• Create a new validation class the make sure required field are either provided in the file or via command line interface (this means we need to make all JCommander required field non-required)

We need to make sure this new feature would not break any existing code.

Alternatives

No response

Anything else?

No response

Are you willing to submit a PR?

• I'm willing to submit a PR!