enhance(surveys): update design + logo + add footnote

[caugner]

Summary

Related to MP-1173. Extracted from #11272.

Problem

The current survey design has some issues and inconsistencies.

Solution

Update the design as follows (in collaboration with @AnujaRajput727):

1. Replace the icon, and increase its size.
2. Remove the border around the survey container.
3. Make the margin between elements consistent (teaser / question / survey).
4. Round the corners of the iframe.
5. Update the color of the question (the summary element).
6. Make the iframe wider.
7. Fix the color of the dismiss icon in dark mode.

Also adds a new optional footnote.

---

Screenshots

Before

After

---

How did you test this change?

Ran yarn dev and opened http://localhost:3000/en-US/docs/Web.

[caugner]

Reviewed by @argl via #11272, from which this was extracted.