add dockerfile_openeuler

[TomNewChao]

No description provided.

[TomNewChao]

目前已经适配了osinfra社区，镜像可以使用：https://jenkins.osinfra.cn/job/etherpad/job/etherpad-test-inner/14/
插件无法生效的原因是通过dockerfile安装的插件没有更新到配置中导致的，所以需要手动添加。而通过admin管理员安装插件则会自动更新
参考osinfra社区：
vim /opt/etherpad-lite/var/installed_plugins.json
{"plugins":[{"name":"ep_etherpad-lite","version":"2.0.1"},{"name":"ep_font_size","version":"0.4.59"},{"name":"ep_font_color","version":"0.0.86"},{"name":"ep_font_family","version":"0.5.44"},{"name":"ep_headings2","version":"0.2.62"},{"name":"ep_themes","version":"0.0.113"}]}