…ariable names.

Selinux tasks were not included by zabbix_web role,
seems that include had been dropped by accident (?) on pull request ansible-collections#979 (v2.0.0)

Restored `include_tasks: selinux.yml` to roles/zabbix_web/tasks/RedHat.yml

Refactor `zabbix_selinux` variable to `zabbix_web_selinux` as variable names should be prefixed with role name,
also to use similar pattern with `zabbix_proxy_selinux` and `zabbix_server_selinux` variables.

Refactor `selinux_allow_*` variable names to correlate with selinux boolean names.

Refactor `zabbix_apache_can_connect_ldap` to `selinux_allow_httpd_can_connect_ldap` as it's not apache specific
and not correlating with actual seboolean name.