ZIG ZAG Traversal of Binary Search Tree [JAVA]

#### This issue is about [Algo/DS Name](link to resource for the Algo/DS).

- [x] Issue Title is in form `Algo/DS Name [Language]`.
- [x] I searched or browsed the repo’s other issues to ensure this is not a duplicate.
- [x] This Algo/DS is worth adding to this repository.
- [x] Assign this issue to me (I want to work on this).
- [x] I ensure that I am not already assigned to 2 or more issues.
- [x] I will send my PR only after I'm assigned to this issue by any maintainer.
- [x] I understand that I will be unassigned from this issue if I fail to send a PR for this within a week.

Kindly assign me this issue under contribute-a-thon'21

The issue requests a Java zig-zag traversal implementation for a binary search tree but names no file, test, or entry point. Start by locating the repository’s existing Java data-structure implementations and their conventions for tree traversals. Done means the requested traversal is added in the appropriate location and follows the project’s established structure.

Written by the indexing model from the issue text.