fix(rcm): update the forking behavior in remote config [backport 2.0]

[avara1986]

Backport 1da4fc4 from #7548 to 2.0

Context

The Remote Configuration Publisher/Subscriber System #5464 restarts all pubsub instances when the application forks (for example, gunicorn workers, uwsgi workers, etc.).

Dynamic Instrumentation needs to update the pubsub instance at this point because the probe mechanism should run in the child process. For that, DI needs the callback as the method of an instance of Debugger, which lives in the child process.

https://github.com/DataDog/dd-trace-py/blob/2.x/ddtrace/debugging/_debugger.py#L276

Problem description

When the application forks and restarts the subscribers, this happens before the debugger updates its callback instance.

10348 starting subscribers
10348 restarting the debugger
10348 register callback 4429382528 <bound method Debugger._on_configuration of Debugger(status=<ServiceStatus.STOPPED: 'stopped'>)> 4406068560 shared_data 4398747792

This results in the registration of the callback in the child processes but the execution of callbacks using the instance of the parent process.

• Parent process: register a callback on_configuration for DI

94621 register callback <bound method Debugger._on_configuration of Debugger(status=<ServiceStatus.STOPPED: 'stopped'>)> PubSub Isntance id: 4363974784 Debugger._on_configuration id: 4360362576

• Child processes: register callbacks on_configuration for DI

94638 register callback <bound method Debugger._on_configuration of Debugger(status=<ServiceStatus.STOPPED: 'stopped'>)> PubSub Isntance id: 4392569856 Debugger._on_configuration id: 4364006016
94639 register callback <bound method Debugger._on_configuration of Debugger(status=<ServiceStatus.STOPPED: 'stopped'>)> PubSub Isntance id: 4392569856 Debugger._on_configuration id: 4364006016
94640 register callback <bound method Debugger._on_configuration of Debugger(status=<ServiceStatus.STOPPED: 'stopped'>)> PubSub Isntance id: 4392569856 Debugger._on_configuration id: 4364006016

• Child processes: exec callbacks.

94621 _exec_callback <bound method Debugger._on_configuration of Debugger(status=<ServiceStatus.RUNNING: 'running'>)> PubSub Isntance id: 4392569856 Debugger._on_configuration id:  4360362576
94638 _exec_callback <bound method Debugger._on_configuration of Debugger(status=<ServiceStatus.RUNNING: 'running'>)> PubSub Isntance id: 4392569856 Debugger._on_configuration id:  4360362576
94639 _exec_callback <bound method Debugger._on_configuration of Debugger(status=<ServiceStatus.RUNNING: 'running'>)> PubSub Isntance id: 4392569856 Debugger._on_configuration id:  4360362576
94640 _exec_callback <bound method Debugger._on_configuration of Debugger(status=<ServiceStatus.RUNNING: 'running'>)> PubSub Isntance id: 4392569856 Debugger._on_configuration id:  4360362576

As a result, we're registering callback id 4364006016 but calling 4360362576 (which is the instance of the parent process).

PR Description

This PR removes the restart of publisher-subscriber instances in Remote Configuration at fork and delegates it to the products that have integration with Remote Config, namely AppSec and Dynamic Instrumentation.

Checklist

• Change(s) are motivated and described in the PR description.
• Testing strategy is described if automated tests are not included in the PR.
• Risk is outlined (performance impact, potential for breakage, maintainability, etc).
• Change is maintainable (easy to change, telemetry, documentation).
• Library release note guidelines are followed. If no release note is required, add label changelog/no-changelog.
• Documentation is included (in-code, generated user docs, public corp docs).
• Backport labels are set (if applicable)

Reviewer Checklist

• Title is accurate.
• No unnecessary changes are introduced.
• Description motivates each change.
• Avoids breaking API changes unless absolutely necessary.
• Testing strategy adequately addresses listed risk(s).
• Change is maintainable (easy to change, telemetry, documentation).
• Release note makes sense to a user of the library.
• Reviewer has explicitly acknowledged and discussed the performance implications of this PR as reported in the benchmarks PR comment.
• Backport labels are set in a manner that is consistent with the release branch maintenance policy
• If this PR touches code that signs or publishes builds or packages, or handles credentials of any kind, I've requested a review from @DataDog/security-design-and-guidance.
• This PR doesn't touch any of that.