Tagging survey questions with web-features

**Background**

[web-features](https://github.com/web-platform-dx/web-features) is a project to define the web platform as a set of features, at a level of granularity similar to caniuse.com, with the main use case being providing [Baseline](https://web.dev/baseline) support data for those features. (We're also working with caniuse.com and not trying to duplicate work.)

Additionally, we're using web-features as an identifier to refer to specific from a variety of contexts. The first is web-platform-tests, where we now have a mechanism to tag tests with a web-features identifier, and then show tests for just that feature on wpt.fyi. ([example](https://wpt.fyi/results/css?label=master&label=experimental&aligned&q=feature%3Anesting))

**Suggestion**

I think it would also be valuable to be able to organize survey results by feature, so that web platform engineering teams could answer questions like "what do we know from public surveys about Subgrid?" The answer is something like this:

- https://mdn.dev/archives/insights/reports/mdn-browser-compatibility-report-2020.html#findings-css-grid
- https://2020.stateofcss.com/en-US/features/layout/#subgrid
- https://2020.stateofcss.com/en-US/opinions/#currently_missing_from_css
- Not checked: State of CSS 2021 and 2022
- https://2023.stateofcss.com/en-US/features/layout/#subgrid
- https://2023.stateofcss.com/en-US/usage/#css_interoperability_features

We could simply collect links like these in web-features, but I think that tagging in the surveys or survey results directly would be a more sustainable approach.

@SachaG in GraphQL API that you already provide for all survey results, is there a place where it would be natural to add a tag for web-features? Concretely, it would mean attaching the string "subgrid" with specific questions, and then some other tool would use the API to get links to all of the results that involve "subgrid". I'd like to explore this, and if it seems worthwhile do it going forward as well, not just retroactively.