Task improvements

[annehaley]

Resolves #187

This PR makes the following improvements to analytics tasks:

• Allow tasks to be disabled for certain deployments using feature flags that can be set via environment variable (e.g. DJANGO_ENABLE_TASK_FLOOD_SIMULATION=0)
• Rename the segment_curbs task to tile2net_segmentation to differentiate it from geoai_segmentation
• Add tags to datasets created by anaytics tasks (which requires the addition of a set_tags function on the dataset model)
• Reformat creation datetimes included in the metadata of datasets created by analytics tasks
• Refactor the load_roads management command / project endpoint into a new analytics task
• Add inputs to the geoai_segmentation task: tile_size, tile_overlap, threshold, smoothing_sigma
• Only install large task requirements in celery container (not django)

[zachmullen]

LGTM other than my question about the django settings imports