Add an option to hide the sequence attachment after it has been played back to the last frame.

Sequence attachments are often used for frame-by-frame animations that appear and then disappear, such as VFX. For example, suppose you want to make the muzzle effect of Spineboy's gun into a sequence. If you set the sequence to Once and play it, the last frame will remain as shown below even after the animation ends:

Simply hiding the attachment will hide this VFX, but if you later want to change the FPS of the sequence or adjust the overall length of the animation by box selecting, the key timing for hiding the attachment may become misaligned because the key positions are not affected by the FPS of the sequence attachment.
Therefore, it would be useful to add an option to the sequence attachment itself that allows the attachment to be hidden at the timing corresponding to the next frame when the last frame has been played back.

**Related forum thread:**
https://esotericsoftware.com/forum/d/28945-request-sequence-attachment-automatic-show-and-hide-the-attachment