add support for experiments

[jakecoffman]

What are you trying to accomplish?

• works with pass in all configured experiments github/dependabot-action#1761

This adds explicit experiment support. In the past we would have had to add an experiment check in the Action and add an environment variable, and then check that in the Proxy.

With this we can skip the step in the Action and just check the experiments input.

Anything you want to highlight for special attention from reviewers?

No production risk here, if the data isn't sent it gets the "zero value" and is blank.

How will you know you've accomplished your goal?

I have another PR that needs an experiment so that's how I'd know!

Checklist

• I have run the complete test suite to ensure all tests and linters pass.
• I have thoroughly tested my code changes to ensure they work as expected, including adding additional tests for new functionality.
• I have written clear and descriptive commit messages.
• I have provided a detailed description of the changes in the pull request, including the problem it addresses, how it fixes the problem, and any relevant details about the implementation.
• I have ensured that the code is well-documented and easy to understand.

[Copilot]

Pull request overview

Adds experiment configuration support so proxy features can directly check job-provided experiment flags.

Changes:

• Adds Experiments to proxy configuration.
• Provides an Enabled helper for boolean flags.
• Tests parsing, enabled/disabled flags, invalid values, and missing experiments.

Show a summary per file

File	Description
internal/config/config.go	Defines experiment configuration and lookup behavior.
internal/config/config_test.go	Verifies parsing and experiment checks.

Review details

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• Files reviewed: 2/2 changed files
• Comments generated: 0
• Review effort level: Balanced