Allow leads to be added to more than one subsequence

Enable the ability to add a lead to a second subsequence. I mean sequentially, not simultaneously.

I use subsequences to send more information to my prospects, but sometimes after they reply (and the subsequence ends), I then want to add them to similar subsequence sending them different information or asking them to book a call. Other times, I will accidentally add them to subsequence and cannot add them again since they've already been added to a subsequence.