[Task] Remove confusing "Command group 'config' is experimental" warning

[Alex-AZPS]

Describe the bug

Running az config set (and likely other az config subcommands) prints a confusing warning on
every invocation:

Command group 'config' is experimental and under development. Reference and support levels: https://aka.ms/CLI_refstatus

az config has been a stable, widely-used command group for a long time (output formatting,
extension settings, broker settings, etc.), so this "experimental" warning is misleading and
confusing to users — it suggests the command group itself may change or break, which isn't
accurate for its current state.

Related command

az config set core.enable_broker_on_windows=false
az config set core.enable_broker_on_windows=true

Steps to reproduce

Run any az config set command:

az config set core.enable_broker_on_windows=false

Errors & debug output

Command group 'config' is experimental and under development. Reference and support levels: https://aka.ms/CLI_refstatus

(Screenshot attached showing this warning printed on every az config set invocation.)

Expected behavior

The az config command group should not print an "experimental" warning. If any specific
subcommand or parameter under az config is genuinely experimental, that warning should be scoped
to just that subcommand/parameter rather than the entire config command group — otherwise please
remove the experimental marking from az config entirely, since it's confusing to customers for a
mature, stable command group.

Environment

PowerShell

Additional context

This came up during an internal discussion about the macOS broker authentication rollout
(core.enable_broker_on_mac / core.enable_broker_on_windows), where the warning noise made the
actual command output harder to read.

[yonzhan]

Thank you for opening this issue, we will look into it.

[microsoft-github-policy-service]

🔔 Routing this issue to @Azure/act-quality-productivity-squad.