More narrowly scope IAM policies

Summary:
Previously, we granted dagit and daemon AmazonECS_FullAccess. This
enabled them to do everything they needed - and then some.

This more narrowly scopes the policies attached to each.

dagit only needs to be able to describe tasks to check if a run can be
terminated and to terminate it.

daemon needs to be able to describe a number of different things about a
task so that it can register new task definitions and trigger task runs.

Both include passrole permissions borrowed from AmazonECS_FullAccess.

Test Plan: Deploy and launch a pipeline

Reviewers: dgibson, max, johann

Reviewed By: dgibson, johann

Differential Revision: https://dagster.phacility.com/D8995