Set package refresh scheduler if possible

[parlt91]

What does this PR change?

This PR was originally part of an L3 but it got closed due to noresponse. In the end I forgot to merge it. I think this change is a valuable addition though, so I think we should still merge it.

Change default/fallback scheduler from (none) to (system)
Set the scheduler on package list refresh action if possible

GUI diff

No difference.

• DONE

Documentation

• No documentation needed:

• DONE

Test coverage

• No tests: already covered (existing tests adapted)

• DONE

Links

Tracks https://github.com/SUSE/spacewalk/issues/21290

• DONE

Changelogs

Make sure the changelogs entries you are adding are compliant with https://github.com/uyuni-project/uyuni/wiki/Contributing#changelogs and https://github.com/uyuni-project/uyuni/wiki/Contributing#uyuni-projectuyuni-repository

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• Re-run test "susemanager_unittests"
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[github-actions]

Suggested tests to cover this Pull Request

• minssh_salt_install_package
• min_deblike_monitoring
• srv_power_management
• min_salt_mgrcompat_state
• srv_sync_channels
• allcli_software_channels_dependencies
• srv_content_lifecycle
• minkvm_guests
• srv_task_status_engine
• srv_patches_page
• srv_logfile
• srv_rename_hostname
• srv_docker_cve_audit
• srv_enable_sync_products
• srv_create_repository
• srv_cobbler_profile
• min_empty_system_profiles
• min_ansible_control_node
• srv_reportdb
• min_retracted_patches
• srv_add_rocky8_repositories
• srv_organization_credentials
• allcli_reboot
• min_bootstrap_ssh_key
• min_deblike_salt_install_package
• buildhost_docker_build_image
• minssh_bootstrap_api
• srv_advanced_search
• srv_cobbler_distro
• srv_scc_user_credentials
• min_rhlike_ssh
• allcli_update_activationkeys
• srv_datepicker
• min_salt_openscap_audit
• srv_change_password
• srv_user_preferences
• srv_cobbler_sync
• min_salt_install_with_staging
• allcli_config_channel
• min_salt_software_states
• srv_channels_add
• min_bootstrap_api
• min_bootstrap_reactivation
• min_rhlike_monitoring
• srv_distro_cobbler
• min_rhlike_salt_install_package_and_patch
• min_config_state_channel_api
• buildhost_osimage_build_image
• srv_group_union_intersection
• allcli_action_chain
• min_salt_pkgset_beacon
• buildhost_bootstrap
• proxy_branch_network
• min_cve_id_new_syntax
• min_deblike_ssh
• srv_check_channels_page
• srv_dist_channel_mapping
• min_config_state_channel
• srv_change_task_schedule
• min_salt_minions_page
• srv_delete_channel_with_tool
• srv_notifications
• min_deblike_remote_command
• sle_ssh_minion
• srv_salt
• min_custom_pkg_download_endpoint
• allcli_software_channels
• srv_maintenance_windows
• sle_minion
• srv_cobbler_buildiso
• minssh_move_from_and_to_proxy
• srv_users
• srv_push_package
• min_docker_api
• srv_check_sync_source_packages
• allcli_system_group
• srv_handle_config_channels_with_ISS_v2
• srv_delete_channel_from_ui
• srv_restart
• srv_power_management_redfish
• srv_user_configuration_salt_states
• min_bootstrap_negative
• min_activationkey
• srv_clone_channel_npn
• min_rhlike_salt
• min_salt_formulas_advanced
• srv_handle_software_channels_with_ISS_v2
• srv_manage_channels_page
• srv_mainpage
• min_salt_migration
• min_recurring_action
• proxy_as_pod_basic_tests
• min_salt_minion_details
• min_salt_lock_packages
• min_deblike_openscap_audit
• srv_check_reposync
• min_check_patches_install
• min_virthost
• srv_power_management_api
• min_move_from_and_to_proxy
• min_project_lotus
• min_config_state_channel_subscriptions
• srv_payg_ssh_connection
• min_timezone
• min_salt_user_states
• srv_activationkey_api
• minssh_ansible_control_node
• min_deblike_salt
• buildhost_docker_auth_registry
• srv_monitoring
• min_deblike_salt_install_with_staging
• min_cve_audit
• min_rhlike_remote_command
• srv_channel_api
• proxy_retail_pxeboot_and_mass_import
• min_bootstrap_script
• min_rhlike_openscap_audit
• srv_docker_advanced_content_management
• srv_salt_download_endpoint
• proxy_register_as_minion_with_script
• min_salt_install_package
• srv_menu
• min_monitoring
• min_change_software_channel
• min_action_chain
• srv_osimage
• srv_first_settings
• minssh_action_chain
• srv_create_activationkey
• min_salt_formulas
• allcli_overview_systems_details
• srv_disable_local_repos_off
• min_ssh_tunnel
• proxy_cobbler_pxeboot
• srv_custom_system_info
• allcli_sanity

[cbbayburt]

I remember this from earlier 👍
Thanks for going through with this