Add translated quick actions (but keep English quick actions at the same time)

• As more and more of GitLab is externalized and people use GitLab in their own language, quick actions become less useful/intuitive.
• For example, in addition to having /label be a quick action to add a label, also support /标记 when you are using GitLab in Simplified Chinese. This makes sense because more and more of the GitLab interface would have 标记 to mean labels, and less and less of it would have the actual English word label. So a user who comes to GitLab using that language would never need to know or care about the term label, and so they actually wouldn't even think to use or be familiar with that quick action. Instead, they would be able to use /标记 intuitively.
• We should keep the default /label quick action in this example because during the transition period and also long-term, many users would still be used to using /label even if they are using GitLab in non-English, and so we shouldn't take that away from them.
• Also, some users may prefer to use GitLab in their own non-English as the interface, but still prefer typing/inputting in English. So being additive would support this.