Add great-tables cheatsheet (as .key, .pdf, .png)

## Contributed Cheatsheet Information Cheatsheet Name: Great Tables 1 sentence description of the contents: This is a one-page cheatsheet for the Python package Great Tables Your Name (as you want to be credited on the website): Richard Iannone A link to your github/website (optional): https://github.com/rich-iannone A link to relevant package documentation (optional): https://posit-dev.github.io/great-tables/ Date created/updated (Month YYYY format): July 2025 <!-- Please keep the below portion in your pull request, and check `[x]` the applicable boxes. --> #### Please be sure you've included the [Creative Commons License](https://creativecommons.org/licenses/by/4.0/): - [x] Add CC-BY-SA Your Name to copywrite under the Creative Commons on the cheatsheet #### Check that you have done the following: - [x] Used descriptive file names, something like package-name.pdf or task-name.pdf and did not include "cheatsheet" in the title. - [x] Included a PDF file of entire cheatsheet. - [x] Included a PNG file of the first page size 1100 x 850 in the pngs folder (for the website thumbnail). - [x] Included a Keynote or PowerPoint or similar file in the relevant folder (helps translators who want to translate your cheatsheet). <!-- NEW OR UPDATED TRANSLATIONS --> <!-- Please fill out the fields below: --> ## Translated Cheatsheet Information Cheatsheet Name: Language: Your Name (as you want to be credited on the website): Date created/updated (Month YYYY format): <!-- Please keep the below portion in your issue, and check `[x]` the applicable boxes. --> #### Check that you have done the following: - [ ] Added the [language abbreviation](https://en.wikipedia.org/wiki/List_of_ISO_639-1_codes) to the file name (ex. data-transformation_es.pdf). - [ ] Included a PDF file of your translated cheatsheet to the translation folders. - [ ] Included a Keynote or PowerPoint file for your translated cheatsheet to the translation folder. - [ ] Not duplicated an existing translation. If an existing translation exists, I have edited it.