async getReferrersHistory() {
        const paidConversionEntries = await this.fetchAllPaidConversionSources();
        const signupEntries = await this.fetchAllSignupSources();

        const allEntries = signupEntries.map((entry) => {
            return {
                ...entry,
                paid_conversions: 0,
                date: moment(entry.date).format('YYYY-MM-DD')
            };
        });

        paidConversionEntries.forEach((entry) => {
            const entryDate = moment(entry.date).format('YYYY-MM-DD');
            const existingEntry = allEntries.find(e => e.source === entry.source && e.date === entryDate);

            if (existingEntry) {
                existingEntry.paid_conversions = entry.paid_conversions;
            } else {
                allEntries.push({
                    ...entry,
                    signups: 0,
                    date: entryDate
                });
            }
        });

        // sort allEntries in date ascending format
        allEntries.sort((a, b) => {
            return moment(a.date).diff(moment(b.date));
        });

        return {
            data: allEntries,
            meta: {}
        };
    }
Return a list of all the attribution sources, with their signup and conversion counts on each date
@returns {Promise<{data: AttributionCountStat[], meta: {}}>}