feat: Added group add/remove for files

[stevedylandev]

Added the ability to either add or remove files from a group

NAME:
   pinata groups - Interact with file groups

USAGE:
   pinata groups command [command options] [arguments...]

COMMANDS:
   create, c  Create a new group
   list, l    List groups on your account
   update, u  Update a group
   delete, d  Delete a group by ID
   get, g     Get group info by ID
   add, a     Add a file to a group
   remove, r  Remove a file from a group
   help, h    Shows a list of commands or help for one command

OPTIONS:
   --help, -h  show help