Can anybody share resources how to setup a state of the art devcontainers locally? I've done it once per repository, but couldn't find a way to have "user" owne

Can anybody share resources how to setup a state of the art devcontainers locally? I've done it once per repository, but couldn't find a way to have "user" owned extensions/themes/settings automatically installed when the container starts (I'm talking about bits that each dev may want to customize).