Showing the progress of loading initial stats

[hawkingrei]

Enhancement

Upon launch, TiDB requires the loading of extensive statistical information for query optimization and index selection, among other functions. This process can be protracted, particularly in instances of substantial data volume or intricate table structures. Users are unable to discern the progress of the loading visually and cannot ascertain its completion.

During TiDB's startup procedure, a progress bar should be displayed to indicate the progress of the statistical information loading.