mgr/dashboard: use __name__ for module-specific logging

mgr/dashboard: use __name__ for module-specific logging

Previously, using a hard-coded logger name like 'rgw_client' created
a top-level logger that bypassed the 'mgr.dashboard' hierarchy.
By switching to __name__, we ensure the logger identity follows the
package structure (e.g., 'mgr.dashboard.services.rgw_client').

Since propagate=True is enabled, this allows log records to flow
upward through the 'mgr' parent loggers, ensuring they are correctly
captured, formatted, and attributed to the dashboard module rather than
falling back to the root logger.

Fixes: https://tracker.ceph.com/issues/74848
Signed-off-by: Nitzan Mordechai <nmordech@ibm.com>