Completion for `Tags` command

- [x] I have fzf 0.23.0 or above
- [x] I have read through https://github.com/junegunn/fzf.vim/blob/master/README.md
- [x] I have read through https://github.com/junegunn/fzf/blob/master/README-VIM.md
- [x] I have read through the manual page of fzf (`man fzf`)
- [x] I have searched through the existing issues

Is there a reason why tag completion with the `:Tags` command hasn't been added to fzf.vim so far?

I have it working with `-complete=tag` added to the `Tags` command and it seems to work well in my testing. However, I'm new to Vimscript and `fzf` so it is likely that I may have overlooked any adverse interactions this introduces. Hence, this issue instead of a PR. If this change sounds good, I can send a PR to add it in. Otherwise, please feel free to close this issue.