Migration guide 0.9-0.10 (#530)

First draft of the 0.10 migration guide.

This is generated by #469 and then modified manually

Since this is easy to generate, I will re-generate it multiple time before release so changing the contents of guides is encouraged, but changing ordering should be done closer to release to avoid dealing with multiple conflicts.

For this migration guide, I added tags for areas of each PR, added a bit of spacing and a line for each heading
![image](https://user-images.githubusercontent.com/8348954/216899165-6f99a25f-e32d-42a4-bad4-8e23c7aac366.png)

This is why there are some css files in this pr.


Co-authored-by: IceSentry <IceSentry@users.noreply.github.com>
Co-authored-by: Carter Anderson <mcanders1@gmail.com>