Drinking tea, why did people do that is the first question. Tea can be used as a medicine or as an intoxicating means. Besides that it serves as a ceremony. „Herbal tea“ actually does not exist, seen from a professional tea point of view: something is a herbal infusion or it is tea; there is no middle way.
From the time, man could cook, there were kinds of herbal infusion, probably mainly for medicine purposes. Many medicinal herbs have (in limited dosis) an intoxicating effect, just like modern coffee and tea still have. Please remember that cafein in the form of coffee is seen as doping by the IOC, reason for the famous Dutch Jan Timman to refrain from playing the Dutch Chess Championship for many years as the Dutch national Chess Union (KNSB) uses the IOC doping rules.
The ‚reading‘ of tea leaves was known by the Romans (Pliny the Older), which does not mean, they drank tea as well. Alexander the Great brought tea along from India, possibly in the shape of tea tablets as they were imported in the 18th-19th century at immense scale to the London Tea Exchange.
There are clues as to that at the Court of Charlemagne, tea was consumed.
Archaeological traces in a pot, glass or kettle do exist, but every time it remains uncertain as to what the drink was used for an din what quantities. Any pot with herbs can be regarded as tea pot but that does not make it one. If you check the stomach contents of bog bodies you will notice a lot of traces of herbes; again it is unclear if this is a means for intoxication, a medicine or otherwise.