gh-131591: Add remote debugging attachment protocol documentation (#132638)

Add a developer-facing document describing the protocol used by
remote_exec(pid, script) to execute Python code in a running process.
This is intended to guide debugger and tool authors in reimplementing
the protocol.

Co-authored-by: Pablo Galindo <pablogsal@gmail.com>

Author: ivonastojanovic

Doc/howto/index.rst

@@ -34,6 +34,7 @@ Python Library Reference.
    mro.rst
    free-threading-python.rst
    free-threading-extensions.rst
+   remote_debugging.rst
 
 General:
 
@@ -66,3 +67,4 @@ Debugging and profiling:
 * :ref:`gdb`
 * :ref:`instrumentation`
 * :ref:`perf_profiling`
+* :ref:`remote-debugging`