Feature Description:
I would like to be able to see easily what proportion of the dynmap is still to generate.
This is specifically useful for initial generation.
Currently something can be computed with the /dynmap stats command so I think it could be easily implemented.
My idea is to divide the number of chunks yet to render in the queue by the total number of chunks already rendered.
For example if my server has 100 chunks, 95 generated and 5 in queue, then the dynmap status is 95% up to date.

• Additional context:
  Exemple :

/dynmap stats
Tile Render Statistics:  terratonic.flat: processed=2747, rendered=2747, updated=2000, transparent=11  terratonic.t: processed=40132, rendered=40132, updated=34718, transparent=308  TOTALS: processed=42879, rendered=42879, updated=36718, transparent=319  Triggered update queue size: 111 + 7035
Active render jobs: Chunk Loading Statistics:  Cache hit rate: 80.24%  Chunks processed: Cached: count=3719984, 0.00 msec/chunk  Chunks processed: Already Loaded: count=25665, 0.64 msec/chunk  Chunks processed: Load Required: count=59498, 0.89 msec/chunk  Chunks processed: Not Generated: count=385739, 0.01 msec/chunk

Something like this could be added to this command, but I think it would be even better with a new command, for example :

/dynmap status
111+7035=7146 tiles queued / 40132 tiles rendered = 83% finished rendering

EDIT : it could also be very interesting to have an approximate progress while being updated for a fullrender/radiusrender etc.