better auto scaling

[vincentsarago]

Right now the autoscaling is based on the number of requests per ecs task

titiler/stack/app.py

Lines 74 to 81 in 89d8d64

	# https://github.com/awslabs/aws-rails-provisioner/blob/263782a4250ca1820082bfb059b163a0f2130d02/lib/aws-rails-provisioner/scaling.rb#L343-L387
	scalable_target.scale_on_request_count(
	"RequestScaling",
	requests_per_target=50,
	scale_in_cooldown=core.Duration.seconds(240),
	scale_out_cooldown=core.Duration.seconds(30),
	target_group=fargate_service.target_group,
	)

This should enable fast scaling UP when number of user are loading tiles, but there might be better configuration.