Update ADK doc according to issue #866 - 2 - runner.run_debug()

[adk-bot]

This pull request adds documentation for the new run_debug() helper method, as requested in issue #866.

Proposed Change:

Added a new section to the getting started guide that explains how to use the run_debug() method. The documentation includes:

• An explanation of the method's purpose and benefits.
• A simple code example demonstrating its usage.
• A comparison of the code required before and after the introduction of run_debug().

[koverholt]

I made comments in the other part of this PR at https://github.com/google/adk-docs/pull/870#pullrequestreview-3423932051.