Add stackplot term entry documentation

[AutoHmn13]

• Add comprehensive stackplot.md documentation for matplotlib.pyplot.stackplot()
• Include syntax, parameters, examples, and FAQ sections
• Add stackplot-example.png image demonstrating sales data visualization
• Follow Codecademy template standards with proper YAML front matter

Description

Created comprehensive documentation for matplotlib's stackplot() method (stackplot.md) following Codecademy's documentation standards to the best of my ability for inclusion in the Docs repository. This included:

• Following Codecademy's YAML Front Matter standard with properly formatted Title, Description, Subjects, Tags, and Catalog Content
• Making a clear and concise descriptive overview of the stackplot() method's purpose of visualizing cumulative data contributions and how those contributions change over time
• Thoroughly defining the method's syntax
• Giving details on all eight of stackplot's parameters including baseline options and **kwargs
• Explaining the list of PolyCollection objects the method produces as a return value
• Providing a practical, basic example of stackplot() being used to visualize sales data for different product types, inclusive of the example's code blocks and graphic display output
• Providing a Codebyte section as an interactive example, per Codecademy's guidelines
• Constructing a comprehensive 6 question and answer FAQ section covering colors, patterns, stacking order, transparency, negative values, and edge styling

Type of Change

• Adding a new term entry, pyplot: stackplot() (Issue [Term Entry] Python matplotlib - pyplot: stackplot() #7812)

Checklist

• All writings are my own.
• My entry follows the Codecademy Docs style guide.
• My changes generate no new warnings.
• I have performed a self-review of my own writing and code.
• I have checked my entry and corrected any misspellings.
• I have confirmed my changes are not being pushed from my forked main branch.
• I have confirmed that I'm pushing from a new branch named after the changes I'm making.

[CLAassistant]

All committers have signed the CLA.

[mamtawardhani]

Hey @AutoHmn13, the entry looks amazing! Just one thing, please also add the image for the example 2 output on this branch and also link it with your PR. Let me know once done, thank you!

[AutoHmn13]

Hi @mamtawardhani - I've updated the existing PR and pushed the requested revisions. Please let me know if you need anything further from me on my end. Thanks!