Add maxHeightDelta setting to exclude stale data

[mrfelton]

This pull request introduces a new configuration option maxHeightDelta to the application, which represents the maximum acceptable difference between the block heights of the most current fee estimates. The maxHeightDelta is added to the DataProviderManager class and is used to filter out data points that don't meet the relevancy threshold criteria. The changes also include the necessary updates to the configuration files and the server setup.

Here are the most significant changes:

Configuration updates:

• README.md: Added a new configuration option settings.maxHeightDelta to the list of available configuration options.
• config/custom-environment-variables.json: Included the maxHeightDelta in the environment variable mapping.
• config/default.json: Added a default value for maxHeightDelta.

Codebase changes:

• src/lib/DataProviderManager.ts: Added maxHeightDelta as a member of the DataProviderManager class. Replaced the getSortedDataPoints method with getRelevantDataPoints that filters out data points based on the maxHeightDelta. [1] [2] [3]
• src/server.tsx: Retrieved maxHeightDelta from the configuration and passed it to the DataProviderManager constructor. [1] [2]

Test updates:

• test/DataProviderManager.test.ts: Updated the test case to match the new behavior.