analytics: support multiple tracking IDs, document UA -> GA4 switch (#1029)

* Issue #1023 - note that GA4 properties are supported

* Issue #1023 - parameterize Google Analytics property script

* Issue #1023 - support a list of multiple Google Analytics tracking IDs in config

* Issue #1023 - update Google Analytics configuration doc

* Fix configuration of multiple Google Analytics properties and simplify type checking

* simplify unnecessary code repetition

* tweak Google Analytics config documentation wording