Request to update Live Migration documentation to account for new changes.

https://docs.atlas.mongodb.com/import/live-import/#source-cluster-security

Some more context: MongoDB 5.0 was recently added as a new destination for Live Migration but there was a new restriction where 5.0 was not able to accept "geoHaystack" indexes. This forced MMS to add a new step to ensure no invalid indexes which requires additional permissions.

Because of this we request docs update the screenshot referencing 3.4+ to include `backup` role as well. Our e2e tests have also been set up to do this as well.