Adding in the evaluate postfix notation using Stack (#2598)

* Create evaluate_postfix_notations.py

Adding in the evaluate postfix notation using Stacks
one of the common use with simple stack question
creating a new file for the data structure of stacks

* Create evaluate_postfix_notations.py

Adding in the evaluate postfix notation using Stacks
one of the common use with simple stack question
creating a new file for the data structure of stacks

* Delete evaluate_postfix_notations.py

* Evaluate postfix expression stack clean approach

Sending in the PR again as the Previous request failed in pre commit

* Update evaluate_postfix_notations.py

* Update evaluate_postfix_notations.py

Made changes as per the required for fixing the failing pre-commits.

* Update evaluate_postfix_notations.py

Made changes as suggested by @cclauss

* Update evaluate_postfix_notations.py

fixed pre-commit fails

* Update evaluate_postfix_notations.py

fixing pre-commit fails

* Update evaluate_postfix_notations.py

Deleted trailing white spaces causing pre-commits to fail

* Update data_structures/stacks/evaluate_postfix_notations.py

Co-authored-by: Christian Clauss <cclauss@me.com>

* Update data_structures/stacks/evaluate_postfix_notations.py

Co-authored-by: Christian Clauss <cclauss@me.com>

Co-authored-by: Christian Clauss <cclauss@me.com>