2022 logo as favicon

[alexcjohnson]

Updating to our current logo. I kept just it as a single favicon.ico file.

There are tons of more complicated things we could do if we wanted to optimize this... our main site plotly.com seems to serve a different file for every browser (on my mac I mostly get .avif or .webp), plus it looks for dark/light mode in the OS. One very simple thing we could do is switch to a .png now that we don't support IE, but that's a bigger project and all we'd really stand to gain is a reduction in file size (this favicon.ico is 15kb, a good favicon.png can be ~1-2kb - we have bigger file size issues than a little 10kb savings!) or better looks in some edge cases where this image gets used at a higher resolution (these don't seem very common, things like making a webpage look like an app on iOS or Android)

• I have added entry in the CHANGELOG.md