docs: review format and size of images and video files

[ssbarnea]

Problem

Our images/videos are huge and low quality, we need to fix them.

All captured raw (unprocessed) screenshots and screencast must be uploaded to our team shared directory on https://drive.google.com/drive/u/0/folders/1XoN3ovUiXSkiyP3bENGHV7YsqYYZEccQ?ths=true using the same filename as the target one, so when we need to recompress them we can do it quickly. This also prevents increasing the size of our git repository with binaries.

Solution

• Replace ~30mb of .gif videos that are part of the embedded walkthroughs with another supported file that minimize the size of the files. Try: webp, webm, mp4.
• Replace existing .gif with .png (static), .webp or .webm if an (avoid removing any images directly used in main README.md file as it would break rendering in marketplaces)
• add .gif to .gitignore to avoid accidental introduction of new gif files
• all screenshots and video should use the default dark color scheme of vscode (consistency)

Additional context

• To convert gif to webp we can use official tools made by google (webp package, installable on macos with brew install webp). This installs gif2webp cli utility.
• To convert mp4 to webp, we should use: TBH

Fixes: AAP-46079