Refactor the Task Roles from each Fargate service to a common nested template

[MikeTheCanuck]

As Michael rightly points out, it would be good to refactor out the duplicative Task Role definition in each of the Fargate service templates into a single common nested template that can be consumed by all Fargate services:
hackoregon/hackoregon-aws-infrastructure#69 (comment)

Examples here:
https://github.com/hackoregon/hackoregon-aws-infrastructure/pull/69/files/13a95b89985366ea2397e47a5661d2d6e85883b8#diff-1b3adc1afead09b44609a4036f7f4c7dR203
https://github.com/hackoregon/hackoregon-aws-infrastructure/pull/69/files/13a95b89985366ea2397e47a5661d2d6e85883b8#diff-4fa1203b0e413fc8dd061ccff4e51668R203