If your column selections is stored in a variable you could possibly use the qIncludeInBookmark property in the variable.
The is actually an example in the documentation where this is done:
I have used this once in a QlikView extension and it worked very well, but I have never tried it in Qlik Sense. I don't think the property is exposed in the client, so you need to implement it yourself. If you do, please share your experiences, this might be interesting for others too.
thanks for your help,
so far I created a variable in the app that will be used to store the state.
and i can change its value from the extension.
Where i need some help now, is how do access the GetProperties,SetProperties methods from the extension ?.
as they available only in the engine API (or backendApi ?)
I tried to google it and i see many questions but did not find very clear answer,
I will be happy to post my solution once i get it working