Present user study/survey to "frequent" users

I kinda brought this up on Slack but wanted to write up some longer-form thoughts here for posterity. This may well also be a bad idea, but I want to hash it out a bit.

If possible, I'd like to ask "frequent" users of the Music app how they use the app (e.g. for #671). For privacy reasons, we want to ensure any interaction with a remote server would be opt-in. We'd also want to ensure we're not spamming users, and I think we'd only really want to ask people who actually _use_ the app—whatever we want to determine that means.

Current thought mulling around in my head:

- Use GSettings to locally log when the app has been opened, e.g. as `last-launch`
- When the app is launched, if it's been less than a week(? but more than a day?) since `last-launch`, iterate a counter, e.g. `frequent-launches`; if it's been more than a week, reset the counter
- If the counter hits 3(?), consider this a frequent user of the app, and show an infobar with a request to fill out a user survey.

An advantage of this approach is that we're "targeting" however we determine frequent users completely client-side and anonymously, and not even doing anything with that data other than showing an opt-in survey. A disadvantage is that it's pretty narrowly limiting the scope of people who would participate.

Other thoughts, in no particular order:

- We probably only want to consider users with items in their library?
- Should we count "plays" instead of "launches"?
- If we really wanted to go nuts, we could do a native, client-side survey that just submits the results to a remote URL; this is more work but would probably be a better overall experience. In that case, we'd need to write/host an open source server-side component instead of using a third-party survey service.
- Regardless, do we want/need some sort of validation to ensure it's actual users who are filling out the survey instead of randos who somehow got the link?