Handle enable_beta_ecosystems boolean setting

[markhallen]

What are you trying to accomplish?

We want to use the enable_beta_ecosystems boolean in dependabot.yml files. We are not currently doing anything with this setting.

This PR will handle and use the enable_beta_ecosystems boolean in the dependabot.yml files and allow us to test with the dry-run script.

Contributes to #6528

Anything you want to highlight for special attention from reviewers?

This is a light touch approach using the existing method of passing experiments through.

How will you know you've accomplished your goal?

Bun updates should be processed when this setting is enabled.

We can test the dry run with:

./bin/dry-run.rb npm_and_yarn dsp-testing/dependabot-bun-public --enable-beta-ecosystems

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.

[kbukum1]

LGTM