Introduce automatic session tracking & enhance default parameters

[Jeehut]

This implements the first 3 Pirate Metrics subtasks:

• SwiftSDK: Persist session data with automatic start/end/duration tracking)
• SwiftSDK: Auto-detect and send new installation
• SwiftSDK: Calculate and send session-related stats like average length, distinct days used etc.

Note that I have expanded upon the requested dayOfWeek, dayOfMonth, and dayOfYear fields and ended up with the following fields (the requirements comment was updated):

• TelemetryDeck.Calendar.dayOfWeek - Integer from 1 (Monday) to 7 (Sunday)
• TelemetryDeck.Calendar.dayOfMonth - Integer from 1 to 31, representing the day of the month
• TelemetryDeck.Calendar.dayOfYear - Integer from 1 to 366 (accounting for leap years), representing the day of the year
• TelemetryDeck.Calendar.weekOfYear - Integer from 1 to 53, representing the week of the year
• TelemetryDeck.Calendar.monthOfYear - Integer from 1 to 12, representing the month
• TelemetryDeck.Calendar.quarterOfYear - Integer from 1 to 4, representing the quarter
• TelemetryDeck.Calendar.hourOfDay - Integer from 1 to 24, representing the hour
• TelemetryDeck.Calendar.isWeekend - Bool, true if Saturday or Sunday, false otherwise

All parameters use the Gregorian calendar and return -1 if the value cannot be calculated.

This PR is merge-ready as it targets the feature/pirate-metrics branch (which is 🚧 until all sub-tasks done).

[kkostov]

@Jeehut Is write a new random session identifier into this property each time a new session begins still possible? e.g. can one provide a starting sessionID? For example, if the app is managing the session, it may want to start with a specific "custom" session rather than have a new UUID being assigned.

Since didSet calls into SessionManager, it's no longer possible to provide a sessionID in config before initializing the client, which means some startup signals/logic may execute with a random UUID before being set to the custom one.

We also have generateNewSession() on the client directly, perhaps the API would be easier if:

• sessionID in config is just a writable property, so one could:

let configuration = TelemetryManagerConfiguration.init(
            appID: appID, salt: salt, baseURL: baseURL)
configuration.sessionID = ...
// ...
TelemetryDeck.initialize(config: configuration)

• Extend or overload generateNewSession() as the path of either resetting a session, or providing a custom session identity generateNewSession(uuid: ...).

• SessionManager is then called internally by the client after initialization, and every time generateNewSession is called.