Introduce automatic session tracking & enhance default parameters (targeting main)

[Jeehut]

This closes https://github.com/TelemetryDeck/PirateMetrics/issues/41.

This is simply the feature/pirate-metrics branch with all the unfinished code made private and all TODO comments removed. The goal is to get the already-implemented and automatically sent TelemetryDeck.Acquisition.newInstallDetected signal shipped early in the SDK so we can already provide the "New Users" insight on our Web dashboard.

Note that all of the code was already approved in #225 and #223, therefore no additional review should be needed. Most of the changes here were only to make SwiftLint happy (as the Signal file got too long, I had to split it up).

[kkostov]

@Jeehut could it be TelemetryDeck.Acquisition.newInstallDetected or are installs and users separate concepts/signals? I plan to work on this tomorrow (TelemetryDeck/KotlinSDK#52) so I can still rename them easily.

[Jeehut]

@kkostov Oh, my mistake, I just noticed that I mentioned the newUserDetected signal in the PR description, whereas I implemented TelemetryDeck.Acquisition.newInstallDetected which is what we had agreed on in our call.

Basically, the detection of a new user could be done but would be way more complicated (and maybe not possible on other platforms) to implement & explain to developers, so we had decided to simply consider a new install as a new user, which in practice is good enough for the purposes of trend analysis. So in practice, these concepts don't differ as the new installs actually are the new users – forget about the newUserDetected signal I had mentioned earlier, I updated the PR description accordingly!

[kkostov]

Awesome, thanks! PR is open.

[winsmith]

Awesome work!