[promtail] Add a log message stating that client level stream lag labels are deprecated (#5850)
[promtail] Add a log message stating that client level stream lag labels are deprecated (#5850)

* Add a log message stating that client level stream lag labels are
deprecated and will not be used.

Signed-off-by: Callum Styan <106b387c595dcc1a235f6eff749ea0675b25b42d@gmail.com>

* Error on startup if a client level stream lag labels value is set.

Signed-off-by: Callum Styan <106b387c595dcc1a235f6eff749ea0675b25b42d@gmail.com>

* fix lint error

Signed-off-by: Callum Styan <106b387c595dcc1a235f6eff749ea0675b25b42d@gmail.com>
grafana/loki,grafana/loki,grafana/loki,grafana/loki,grafana/loki,grafana/loki