Adds timeseries support to Issue type widgets in dashboards. Feature is gated on the displayType dropdown by checking for the dashboards-issue-widget-series-display-type feature flag.

Current feature limitations:

• Currently for Issue timeseries widgets, only count(new_issues) and count(resolved_issues are supported yAxes.
• Query search filtering is not supported by the backing endpoint (TODO: hide this element in the UI)
• Group by is supported by the endpoint, but only by release (TODO: this is not yet added to the UI, handle in follow up PR)

Implementation notes:

• Uses the new /issues-timeseries endpoint
  • Adds a new IssuesSeriesResponse type to match the response payload received in the frontend
  • Due to the /issues-timeseries endpoint not sharing query parameters with the /issues endpoint for tables, specialized logic has been added to handle resetting the widget builder state when switching between table and series display types:
    • typeSelector.tsx has been updated to reset the current query state on change
    • generateIssueWidgetFieldOptions updated to accept display type and return results based on table or series display
  • Adds new options to widget dataset configs:
    • defaultSeriesField which represents the default field for a series/chart display widget. Used as the default when adding a new yAxis to an Issue series widget.
    • defaultSeriesWidgetQuery which represents the default widget query for a series/chart display. This is used for Issue widgets when switching between table and series display views to set the default query.