Allow a context generator to return an array object for use in addGlobalContexts()

[rlh1994]

Is your feature request related to a problem? Please describe.
I may have multiple global contexts that depend on some globalstate/the event type/schema etc. Currently to have multiple global contexts be dynamically generated I have to create a generating function for each context and then combine them in an array in the addGlobalContexts() call, as a single generating function that returns a list does not work (no contexts are tracked).

Describe the solution you'd like
addGlobalContexts() to take as an input acontextGenerator type function that returns an array object

Describe alternatives you've considered
Creating multiple contextGenerator type functions and passing an array of them to addGlobalContexts() e.g. addGlobalContexts([contextGenerator1, contextGenerator2, ...])

Additional context
Relevant docs https://docs.snowplow.io/docs/collecting-data/collecting-from-own-applications/javascript-trackers/browser-tracker/browser-tracker-v3-reference/tracking-events/#context-generators