Update ECS Worker Guide worker policies

[EmilRex]

The ECS Worker Guide instructs users to assign the arn:aws:iam::aws:policy/service-role/AmazonECSTaskExecutionRolePolicy policy to their worker ECSTask, but this role is insufficient for actually starting flow runs ECSTasks. The role should include the following permissions (also defined here):

"ec2:DescribeSubnets",
"ec2:DescribeVpcs",
"ecr:BatchCheckLayerAvailability",
"ecr:BatchGetImage",
"ecr:GetAuthorizationToken",
"ecr:GetDownloadUrlForLayer",
"ecs:DeregisterTaskDefinition",
"ecs:DescribeTaskDefinition",
"ecs:DescribeTasks",
"ecs:RegisterTaskDefinition",
"ecs:RunTask",
"ecs:StopTask",
"iam:PassRole",
"logs:CreateLogGroup",
"logs:CreateLogStream",
"logs:GetLogEvents",
"logs:PutLogEvents"