Adds support for instance profile credentials to the controller.

[tlm]

This PR adds support to the controller for using AWS instance profiles attached to its machine. With this change we have introduced a new credential type and blocking to make sure the instance profile is attached to the controller's machine.

Checklist

• Requires a pylibjuju change
• Added integration tests for the PR
• Added or updated doc.go related to packages changed
• Comments answer the question of why design decisions were made

QA steps

1. Create a new instance profile

aws iam create-instance-profile --instance-profile-name tlm-ip-test
{
    "InstanceProfile": {
        "Roles": [],
        "InstanceProfileName": "tlm-ip-test",
        "Path": "/",
    }
}

2. Add a role to the instance profile. THIS MUST BE DONE or the boostrap will hang in waiting for association.

aws iam add-role-to-instance-profile --instance-profile-name tlm-ip-test --role-name <role_name>

3. Do the bootstrap with:

juju bootstrap --bootstrap-constraints="instance-role=tlm-ip-test" aws/ap-southeast-2 test-ip-controller

NOTE: the auto keywork to instance-role will work in create an instance profile for the controller but the bootstrap will hang as we currently don't have the role sorted for the controller yet so we must create it our selves until the next PR.

[wallyworld]

A few small things, looks like good progress

[tlm]

$$merge$$

[tlm]

$$merge$$