Update Experimenter for Firefox Labs to rename or expand "Fluent ID"

[data-sync-user]

Experimenter uses the words “Fluent ID” to refer to the in-tree slugs for a given experiment. Android doesn’t use Fluent and uses strings from strings.xml. Called the slug or string reference ID in Android.

Recommend updating the wording to expand the types or make it more cross-platform generic phrasing.

┆Issue is synchronized with this Jira Task

[data-sync-user]

Olivia Hall commented from Jira:

Some of the docs reference this screen directly and list “Fluent ID” as a literal, they might need an update or at least a second look with this change too.