[AC-225] Add array-mapping for selectors

[jdkula]

Allows selectors of the format .arrayfield[].subfield which applies the mapping following [] to all the elements of the array identified by the mapping preceding it. For example, selecting .collections[].name on {collections: [{name: "a"}, {name: "b"}]} would return ["a", "b"].

Also uses it to provide an additional default selector for integrations

[linear]

AC-225 more selectors needed

see TODO in cli/format/integration.go

[pmenglund]