[Feature request] Add options to improve annotation visibility

**Why is this needed**: Annotations do not scale well (at all?) with panel size, which makes it nearly impossible to notice them on large, screen-wide panels. The best way to understand the problem is by looking at the screenshot below: <img width="1394" height="730" alt="Image" src="https://github.com/user-attachments/assets/0476d5da-8eb9-4a96-a905-0ab29fc06e17" /> This is a status history panel and the whole dashboard is basically this one panel. There are two annotations on it, but I hope you see that they are barely noticeable. Currently, there is only one thing you can change about annotations and it is the color. I tried multiple different colors and this light-blue is the best (in terms of visibility) that I found. **What would you like to be added**: I would like to have more options to customize how annotations look, something to make them more visible. Some ideas: 1. A slider to change dash line thickness. 2. A toggle to enable an outline. 3. An option to select where the bottom triangle (the one that shows annotation text on hover) appears on the panel (top, bottom or both). **Who is this feature for?** All users, I guess.