Set up translation for Duo Chat component and all sub-components

Since we are displaying the DuoChat component in a completely translated interface, we should ensure that the DuoChat UI is also translatable.

Proposal:

Every hardcoded string that is user-facing and located under: gitlab-ui/src/components/experimental/duo/chat

Should be made translation-ready using the tools we already have in place:

https://gitlab.com/gitlab-org/gitlab-ui/-/blob/main/doc/contributing/translation.md