Auto-detect and send new installation

[kkostov]

Related to TelemetryDeck/SwiftSDK#225

"New installation" - when the SDK is started and no previous sessions are detected in local storage e.g.

    // if the recent sessions are empty, this must be the first start after installing the app
        if self.recentSessions.isEmpty {
            // this ensures we only use the date, not the time –> e.g. "2025-01-31"
            let todayFormatted = ISO8601DateFormatter.string(from: Date(), timeZone: .current, formatOptions: [.withFullDate])

            self.firstSessionDate = todayFormatted

            TelemetryDeck.internalSignal(
                "TelemetryDeck.Acquisition.newInstallDetected",
                parameters: ["TelemetryDeck.Acquisition.firstSessionDate": todayFormatted]
            )
        }