Refactor: Enhance WebstatusLineChartPanel with data fetching, aggregation, and additional series calculations

[jcscottiii]

This PR significantly enhances the WebstatusLineChartPanel abstract class by adding functionality for data fetching, aggregation, and calculation of additional series. These improvements streamline the creation of line chart panels and promote code reuse across different parts of the application. A lot of these changes come from or are inspired by things in the feature detail page. The removal of that code will come in the next PR when those charts implement WebstatusLineChartPanel.

Key changes:

• _fetchAndAggregateData method: This new method centralizes the logic for fetching data from multiple sources, applying additional series calculations, and dispatching events. It simplifies the implementation of subclasses by handling common tasks like:
  • Fetching data concurrently using FetchFunctionConfig objects.
  • Applying SeriesCalculator functions to calculate additional series data based on AdditionalSeriesConfig configurations.
  • Dispatching data-fetch-starting and data-fetch-complete events to communicate data fetching progress and results.
• FetchFunctionConfig and AdditionalSeriesConfig: These interfaces provide a structured way to define data sources and additional series calculations, promoting consistency and maintainability.
• calculateMax calculator/aggregator: This utility function calculates the maximum value for each timestamp across multiple series, enabling easy creation of "Total" or "Max" series in charts.
• LineChartMetricData enhancements:
  • Added an optional getTooltip method to allow customization of tooltips for individual data points.
  • Borrowed the timestampExtractor and valueExtractor concepts from the feature detail page charts to provide more flexibility in handling different data structures.
• Improved loading and error states:
  • Set a minimum height of 300px for loading and error states to match the chart height and reduce jank.
  • Added a centered spinner and message to the loading state for a better user experience.
• Removed multiple selection mode: Removed the multiple selection mode in the common Google chart settings to align with the behavior of feature detail page charts.
• Refactored WebstatusStatsGlobalFeatureCountChartPanel and WebstatusStatsMissingOneImplChartPanel: These classes now use the _fetchAndAggregateData method, simplifying their code and removing the need to handle pages of data manually.
• Other UI changes: Removed the header divider line between chart title and chart to be consistent with feature detail charts.

This PR improves the WebstatusLineChartPanel class's functionality and reusability, making it easier to create and maintain various line chart panels across the application. It also enhances the user experience with better loading and error states and promotes consistency by aligning chart behavior.