feature request: Better option for obtaining Agent Evaluation results in a JSON file

[Neutrollized]

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Contribution guide.

Is your feature request related to a problem? Please describe.
I'm unable to obtain Agent Evaluation (adk eval) results in JSON format/file.

Describe the solution you'd like
An additional option to pass to adk eval such as: --results_output_file FILENAME.json so we can obtain a printed results in JSON format.

Describe alternatives you've considered

Alternative 1

The best option currently is to run adk eval with the --print_detailed_results option and redirect the output to a file, i.e.:

adk eval \
    --config_file_path eval/data/test_config.json \
    --print_detailed_results \
    my_agent \
    eval/data/my_test.evalset.json

However, this output will contain a summary from the test result that are not JSON and I would have to delete the first dozen lines or so in the output to get what I want.

Alternative 2

Another alternative (which is terrible in its current form) is to run the eval set from adk web, but there are a lot of issues with this method:

1. Eval Set file needs ot be in the same directory as your agent module
2. There's no way to pass in a test_config.json with criteria config, and so the tool trajectory is set at 1.0 and no option to specify a response matching score
3. output goes to a folder .adk/eval_history/ in the agent module directory and the file is a .json file, except everything double-quote in there is escaped with a backslash (i.e. ") and it's not easy to read. I had to get another Python script to strip out the escape backslashes and return the json.loads(CLEANED_DATA) before it's usable.

Additional context
I wrote a Medium article about Agent Evaluation with ADK and this was a question that came up, so I thought I'd turn it into a GitHub issue 😆

[wyf7107]

You can try useing the adk web and eval tab to run and create evaluation. Then there will be json file generated in your folders

[Neutrollized]

Yes, and I already mentioned that in Alternative 2, but there are a lot of issues with using that method, which I've also listed.