Allow configurable default time range and series limit in dashboards

Currently, OpenReplay dashboards have two hardcoded limitations that affect user experience:

1. Time range always resets to "Last 24 Hours": Every time a user navigates to a dashboard, the time range selector resets to the default "Last 24 Hours", even if they previously selected a different range (e.g., "Last 7 Days").

2. Maximum 3 series per chart: Dashboard widgets are limited to displaying a maximum of 3 data series per chart.

Time Range Reset:

• File: frontend/app/mstore/dashboardStore.ts
• Lines: 27-30
• Code:

period: Record<string, any> = Period({ rangeName: LAST_24_HOURS });
drillDownFilter: Filter = new Filter();
comparisonFilter: Filter = new Filter();
drillDownPeriod: Record<string, any> = Period({ rangeName: LAST_24_HOURS });

The LAST_24_HOURS constant is hardcoded in the constructor, and there's no persistence mechanism (like localStorage) to remember user preferences.

Series Limit:

• File: frontend/app/components/Dashboard/components/WidgetForm/WidgetFormNew.tsx
• Line: 98
• Code:

const canAddSeries = metric.series.length < 3;

• Line: 192 - User-facing message:

<Tooltip
  title={canAddSeries ? '' : t('Maximum of 3 series reached.')}
>