WL#17235: Make "GR: Flow-control metrics" community edition

# EXECUTIVE SUMMARY

This worklog makes the existing `GR: Flow-control metrics` available in the
MySQL Community Edition.

These metrics, exposed through the `group_replication_flow_control_stats`
component, provide deeper visibility into Group Replication flow-control
behavior. The change aligns feature availability between Community and
Enterprise editions without introducing new functionality or altering existing
behavior.

# USER STORIES

* As a MySQL Community Edition admin, I want visibility into Group Replication
  flow-control behavior to help tune group replication performance.

# FUNCTIONAL REQUIREMENTS

FR-01. The `GR: Flow-control metrics` feature shall be available in the
       MySQL Community Edition build.

FR-02. The feature shall expose the same set of Flow-control
       in the Community Edition as currently available in the Enterprise
       Edition.

FR-03. The feature shall be available in Community Edition builds, consistent
       with current behavior in Enterprise Edition builds.

FR-04. Existing interfaces (e.g., performance schema tables, status variables,
       or instrumentation points) used to expose the stats shall remain
       unchanged.

FR-05. The change shall be transparent to users upgrading from earlier versions,
       with no configuration changes required.

FR-06. There shall be no functional regressions or behavior changes to group
       replication, or performance when the feature is enabled.

FR-07. The implementation shall maintain compatibility across supported
       platforms for Community Edition builds.

# NON-FUNCTIONAL REQUIREMENTS

NFR-01. Logging, error handling, and diagnostics behavior shall remain
        unchanged.

# Summary of the approach

This worklog makes the existing `GR: Flow-control metrics` feature available in
the MySQL Community Edition build.
The implementation reuses the current instrumentation and logic without
introducing new functionality. The change is limited to build and packaging
adjustments to ensure the feature is included in Community Edition binaries,
consistent with its behavior in the Enterprise Edition.

No changes are made to group replication logic, metrics collection, or
exposure mechanisms.

# Security context

No applicable changes on security context.

# Observability

Observability remains unchanged.

# Upgrade/downgrade and cross-version replication

Upgrades from earlier Community Edition versions will automatically gain access
to the Group Replication flow-control stats, without requiring configuration
changes.

Downgrades behave as before; stats not supported by the downgraded version
will simply be unavailable.

Cross-version replication behavior is unchanged.

There is no impact on group replication compatibility between Community and
Enterprise Edition instances.

# User interface

No new user interfaces are introduced.

Existing SQL interfaces, system tables, and performance schema views remain
unchanged.

Users interact with the feature using the same queries and tools as before.

# Deployment and installation

The change affects build and packaging only.

Community Edition binaries will include the feature by default.

No special installation steps are required.

Deployment workflows remain unchanged.

# Protocol

No protocol changes.

# Failure Model Specification

No new failure modes are introduced.

# Behavior Changes

The only behavior change is the availability of Group Replication flow-control
stats in Community Edition.

There are no changes to group replication behavior, stats semantics, or
default configurations.

Enterprise Edition behavior remains unchanged.