I didn't know this was associated with The Office. I thought it had been around for years. It just means that's there's always something happening. No peaceful moments.
DOCTOR IN THE HOUSE: IT'S ALL GO.../THE STUDENTS ARE REVOLTING (1969)
The phrase was certainly used in 'Round the Horne' 40 odd years ago. Can't remember if it was one of Kenneth Williams' characters or not. It used to be said in a very weary voice.
The earliest recorded use of the words was in a New Statesman article published in 1967 which read, "Believe me, it's all go with these *******, mate. Life's just one frenetic whirl of soign� secretaries and sex-mad air 'ostesses."
The words 'frenetic whirl' pretty well sum up exactly what 'it's all go' means.
Oh dear! The asterisked-out word is one that means 'business magnates'. It opens with the letters 'ty' and ends with a word that is also used to refer to people of colour.
Isn't it amazing? No-one would even have noticed but for the editing!