Implement `head()` function for a Singly Linked List

[ashikka]

Taking reference from issue #12, implement the head() function for a Singly Linked List. This function will find the element at the head of the list.

First step

Search, read, and understand information about lists, linked lists, and singly-linked lists, and how they are implemented.

Second step

Open a pull request with the data structure implementation, and wait for comments from @code-sherpas/kollections-maintainers.

Minimum acceptance criteria

• The implementation must be well documented with proper Javadoc at Class and function levels.
• The implementation must be tested with automatic tests that cover all relevant cases and situations.
• The implementation must be generic.
• The implementation must have the expected time complexity according to Computer Science. Here you can find a very helpful cheat sheet.

Related resources:

• https://www.youtube.com/watch?v=v4cd1O4zkGw&ab_channel=HackerRank
• https://www.youtube.com/watch?v=njTh_OwMljA&ab_channel=HackerRank
• https://en.wikipedia.org/wiki/List_(abstract_data_type)
• https://en.wikipedia.org/wiki/Linked_list#Singly_linked_list
• https://www.bigocheatsheet.com/

[bhaveesarna]

Hey @ashikka could I work on this?