Added new OpenAI SVG files and renamed existing one

[justinle]

• Added two new SVG files for OpenAI and the OpenAI API platform logo
• Renamed the existing chatgpt.svg to openai-chatgpt.svg to more closely follow existing naming convention

Requirements

Go over all the following points, and put an x in all the boxes that apply.

• My issuer icon is fully vector and does not contain (parts of) a JPG/PNG/etc.
• My issuer icon contains the original brand logo, not that from an icon pack.
• My issuer icon is somewhat square, so it's nicely visible in the app.
• My issuer icon starts and ends with the <svg> element.
• My issuer icon is scalable (it uses viewBox instead of a static width/height).
• My issuer icon does not contain whitespace around the SVG (this JSFiddle could help to remove whitespace).
• My issuer icon does not include the doctype element.
• My issuer icon directory and file name is lowercase.
• My issuer icon directory and file are in the vectors/[domain name]/ folder.
• My pull request contains just one icon.