Allow slashes in the role assumption.

[zaphinath]

Is your feature request related to a problem? Please describe.
A clear and concise description of what the problem is. Ex. I'm always frustrated when [...]
When I need to assume a role into an account that isn't just ACCOUNT:role/name -- instead it is ACCOUNT:service-role/name it doesn't auto populate that in the UI. The switch accounts section of AWS just has the "name" and not "service-role/name". In this case the "service-role" needs to be added manually.

Describe the solution you'd like
A clear and concise description of what you want to happen.
Is there a way that if the role isn't standard that it could copy the whole target over? In the above example it would be "service-role/name" to the UI instead of just "name"

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.
Right now just need to manually remember the accounts that are like this.

Additional context
Add any other context or screenshots about the feature request here.

[profile admin-externaldns]
role_arn = arn:aws:iam::123456789 :service-role/external-dns
role_name = service-role/external-dns
target_role_name = service-role/external-dns
region = us-east-1
color = f20707