Add support for `positionInList` input variable within `epicMoveList` mutation

Summary

We support positionInList within issueMoveList mutation which allows us to support Move to start of list & Move to end of list actions on Issue cards within Issue Boards.

These actions are also available for Epics within Epic Boards but they don't work since positionInList input variable is not supported on epicMoveList mutation.

Docs Support

For issues requiring an update to GitLab docs, please note that this is part of the definition of done for this issue. Please create a separate MR for the docs update related to the MR for the actual change to ensure code reviews are not blocked by TW reviews.

• This issue requires an update to GitLab docs
• This issue does not require an update to GitLab docs