RAW does not allow you to do it.
Rules As Written means something must be Written concerning it. There is nothing written regarding action surge and extra attack, there is nothing written stating that you can't do this specifically and there also is nothing written that states something is assumed not allowed unless it is specifically allowed. That too is not Rules As Written.
As a basic premise, for something to be "RAW" there has to be written rules concerning it. Do you not understand that concept?
Drinking is allowed by RAW.
But drinking milk is not allowed because milk is not mentioned specifically. Sure they can drink something, just like they can use action surge, but RAW they can't drink milk. I think by your version of RAW they can drink water, wine and ale as I think all three of those things are mentioned specifically, although you could argue they are restricted to certain races as some of them are only mentioned in context to a specific race.
There are opther things that can be bought, but they can't be drank .... at least not RAW.
Also those quotes you gave did not specify the fighter class, so they are not doable by fighters.
"Even in such cases, the kobolds' fear of retaliation usually prevents them from trying to directly harm the gnomes, but they might spit in the milk.
Kobolds can absolutely spill milk, just like my fighter can absolutely action surge. The question though is can they DRINK milk. RAW they can't because it is not specifically mentioned right?
Not as far as drinking it isn't.So even milk is written.![]()