client: docker: add exec wrapper, update completion

client/src/docker/docker.bash

@@ -77,6 +77,7 @@ function main()
 
     run         \e[34;3mSpawn docker-finance container with given command (container removed on exit)\e[0m
     shell       \e[34;3mOpen shell into running docker-finance container\e[0m
+    exec        \e[34;3mExecute command within running docker-finance container\e[0m
 
     plugins     \e[34;3mExecute a client-side categorical docker-finance plugin ('repo' or 'custom')\e[0m
     version     \e[34;3mPrint current version of docker-finance and its dependencies\e[0m
@@ -203,6 +204,9 @@ function main()
     shell)
       lib_docker::shell "${@:3}"
       ;;
+    exec)
+      lib_docker::exec "${@:3}"
+      ;;
     backup)
       lib_docker::backup "${@:3}"
       ;;